diff --git a/app/Activity/Actions/ActivityUpdateAction.php b/app/Activity/Actions/ActivityUpdateAction.php
index ce7f7f5f..41b18c89 100644
--- a/app/Activity/Actions/ActivityUpdateAction.php
+++ b/app/Activity/Actions/ActivityUpdateAction.php
@@ -3,6 +3,7 @@
 namespace App\Activity\Actions;
 
 use App\Activity;
+use App\Member\Membership;
 use App\Subactivity;
 use Illuminate\Http\RedirectResponse;
 use Illuminate\Support\Facades\DB;
@@ -46,6 +47,12 @@ class ActivityUpdateAction
             $this->validateNami($activity, $request->validated());
         }
 
+        $removingSubactivities = $activity->subactivities()->whereNotIn('id', $request->validated('subactivities'))->pluck('id');
+
+        if ($removingSubactivities->first(fn ($subactivity) => Membership::firstWhere(['activity_id' => $activity->id, 'subactivity_id' => $subactivity]))) {
+            throw ValidationException::withMessages(['subactivities' => 'Untergliederung hat noch Mitglieder.']);
+        }
+
         $this->handle($activity, $request->validated());
 
         return redirect()->route('activity.index');
diff --git a/app/Activity/Api/SubactivityUpdateAction.php b/app/Activity/Api/SubactivityUpdateAction.php
new file mode 100644
index 00000000..82f8ebba
--- /dev/null
+++ b/app/Activity/Api/SubactivityUpdateAction.php
@@ -0,0 +1,93 @@
+<?php
+
+namespace App\Activity\Api;
+
+use App\Activity;
+use App\Member\Membership;
+use App\Subactivity;
+use Illuminate\Http\JsonResponse;
+use Illuminate\Support\Arr;
+use Illuminate\Validation\Rule;
+use Illuminate\Validation\ValidationException;
+use Lorisleiva\Actions\ActionRequest;
+use Lorisleiva\Actions\Concerns\AsAction;
+
+class SubactivityUpdateAction
+{
+    use AsAction;
+
+    /**
+     * @param array<string, string|array<int, int>> $payload
+     */
+    public function handle(Subactivity $subactivity, array $payload): Subactivity
+    {
+        $subactivity->update(Arr::except($payload, 'activities'));
+
+        if (null !== data_get($payload, 'activities')) {
+            $subactivity->activities()->sync($payload['activities']);
+        }
+
+        return $subactivity;
+    }
+
+    /**
+     * @return array<string, string>
+     */
+    public function rules(): array
+    {
+        return [
+            'name' => ['required', 'string', 'max:255', Rule::unique('subactivities', 'name')->ignore(request()->route('subactivity')->id)],
+            'activities' => ['present', 'array', 'min:1'],
+            'is_filterable' => 'present|boolean',
+        ];
+    }
+
+    /**
+     * @return array<string, string>
+     */
+    public function getValidationAttributes(): array
+    {
+        return [
+            'activities' => 'Tätigkeiten',
+        ];
+    }
+
+    public function asController(ActionRequest $request, Subactivity $subactivity): JsonResponse
+    {
+        if ($subactivity->hasNami) {
+            $this->validateNami($subactivity, $request->validated());
+        }
+
+        $removingActivities = $subactivity->activities()->whereNotIn('id', $request->validated('activities'))->pluck('id');
+
+        if ($removingActivities->first(fn ($activity) => Membership::firstWhere(['activity_id' => $activity, 'subactivity_id' => $subactivity->id]))) {
+            throw ValidationException::withMessages(['activities' => 'Tätigkeit hat noch Mitglieder.']);
+        }
+
+        return response()->json($this->handle($subactivity, $request->validated()));
+    }
+
+    /**
+     * @todo handle this with a model event on the pivot model
+     *
+     * @param Payload $payload
+     */
+    private function validateNami(Subactivity $subactivity, array $payload): void
+    {
+        if ($subactivity->name !== $payload['name']) {
+            throw ValidationException::withMessages(['name' => 'Untertätigkeit ist in NaMi. Update des Namens nicht möglich.']);
+        }
+
+        $removingActivities = $subactivity->activities()->whereNotIn('id', $payload['activities'])->pluck('id');
+
+        if ($removingActivities->first(fn ($activity) => Activity::find($activity)->hasNami)) {
+            throw ValidationException::withMessages(['activities' => 'Tätigkeit kann nicht entfernt werden.']);
+        }
+
+        $addingActivities = collect($payload['activities'])->filter(fn ($activityId) => $subactivity->activities->doesntContain($activityId));
+
+        if ($addingActivities->first(fn ($activity) => Activity::find($activity)->hasNami)) {
+            throw ValidationException::withMessages(['activities' => 'Tätigkeit kann nicht hinzugefügt werden.']);
+        }
+    }
+}
diff --git a/routes/web.php b/routes/web.php
index f1e80122..29279cc3 100644
--- a/routes/web.php
+++ b/routes/web.php
@@ -7,6 +7,7 @@ use App\Activity\Actions\DestroyAction as ActivityDestroyAction;
 use App\Activity\Actions\EditAction as ActivityEditAction;
 use App\Activity\Actions\IndexAction as ActivityIndexAction;
 use App\Activity\Api\SubactivityStoreAction;
+use App\Activity\Api\SubactivityUpdateAction;
 use App\Contribution\Actions\FormAction as ContributionFormAction;
 use App\Contribution\ContributionController;
 use App\Course\Controllers\CourseController;
@@ -62,4 +63,5 @@ Route::group(['middleware' => 'auth:web'], function (): void {
     Route::patch('/activity/{activity}', ActivityUpdateAction::class)->name('activity.update');
     Route::delete('/activity/{activity}', ActivityDestroyAction::class)->name('activity.destroy');
     Route::post('/subactivity', SubactivityStoreAction::class)->name('api.subactivity.store');
+    Route::patch('/subactivity/{subactivity}', SubactivityUpdateAction::class)->name('api.subactivity.update');
 });
diff --git a/tests/Feature/Activity/SubactivityTest.php b/tests/Feature/Activity/SubactivityTest.php
index 4cf14c33..3ce15525 100644
--- a/tests/Feature/Activity/SubactivityTest.php
+++ b/tests/Feature/Activity/SubactivityTest.php
@@ -3,6 +3,8 @@
 namespace Tests\Feature\Activity;
 
 use App\Activity;
+use App\Member\Member;
+use App\Member\Membership;
 use App\Subactivity;
 use Illuminate\Foundation\Testing\DatabaseTransactions;
 use Tests\TestCase;
@@ -86,4 +88,191 @@ class SubactivityTest extends TestCase
         ]);
         $this->assertDatabaseMissing('subactivities', ['nami_id' => 556]);
     }
+
+    public function testItCannotUpdateNameIfInNami(): void
+    {
+        $this->login()->loginNami();
+        $activity = Activity::factory()->inNami(123)->create();
+        $subactivity = Subactivity::factory()->hasAttached($activity)->name('abc')->inNami(777)->create();
+
+        $response = $this->patchJson(route('api.subactivity.update', ['subactivity' => $subactivity->id]), [
+            'name' => 'aaaa',
+            'nami_id' => 777,
+            'activities' => [$activity->id],
+            'is_filterable' => false,
+        ]);
+
+        $response->assertJsonValidationErrors(['name' => 'Untertätigkeit ist in NaMi. Update des Namens nicht möglich.']);
+    }
+
+    public function testItCannotUpdateNamiId(): void
+    {
+        $this->login()->loginNami();
+        $activity = Activity::factory()->inNami(123)->create();
+        $subactivity = Subactivity::factory()->hasAttached($activity)->name('abc')->inNami(777)->create();
+
+        $response = $this->patchJson(route('api.subactivity.update', ['subactivity' => $subactivity->id]), [
+            'name' => 'abc',
+            'nami_id' => 556,
+            'activities' => [$activity->id],
+            'is_filterable' => false,
+        ]);
+
+        $this->assertDatabaseHas('subactivities', [
+            'id' => $subactivity->id,
+            'nami_id' => 777,
+        ]);
+    }
+
+    public function testItCannotSetNamiId(): void
+    {
+        $this->login()->loginNami();
+        $activity = Activity::factory()->inNami(123)->create();
+        $subactivity = Subactivity::factory()->hasAttached($activity)->name('abc')->create();
+
+        $response = $this->patchJson(route('api.subactivity.update', ['subactivity' => $subactivity->id]), [
+            'name' => 'abc',
+            'nami_id' => 556,
+            'activities' => [$activity->id],
+            'is_filterable' => false,
+        ]);
+
+        $this->assertDatabaseHas('subactivities', [
+            'id' => $subactivity->id,
+            'nami_id' => null,
+        ]);
+    }
+
+    public function testItCanUpdateIsFilterableIfInNami(): void
+    {
+        $this->login()->loginNami();
+        $activity = Activity::factory()->inNami(123)->create();
+        $subactivity = Subactivity::factory()->hasAttached($activity)->name('abc')->filterable()->inNami(777)->create();
+
+        $response = $this->patchJson(route('api.subactivity.update', ['subactivity' => $subactivity->id]), [
+            'name' => 'abc',
+            'activities' => [$activity->id],
+            'is_filterable' => false,
+        ]);
+
+        $this->assertDatabaseHas('subactivities', [
+            'id' => $subactivity->id,
+            'is_filterable' => false,
+        ]);
+    }
+
+    public function testItCanUpdateNameWhenNotInNami(): void
+    {
+        $this->login()->loginNami();
+        $activity = Activity::factory()->inNami(123)->create();
+        $subactivity = Subactivity::factory()->hasAttached($activity)->name('abc')->create();
+
+        $response = $this->patchJson(route('api.subactivity.update', ['subactivity' => $subactivity->id]), [
+            'name' => 'def',
+            'activities' => [$activity->id],
+            'is_filterable' => false,
+        ]);
+
+        $this->assertDatabaseHas('subactivities', [
+            'id' => $subactivity->id,
+            'name' => 'def',
+        ]);
+    }
+
+    public function testNameShouldBeUnique(): void
+    {
+        $this->login()->loginNami();
+        $activity = Activity::factory()->inNami(123)->create();
+        $subactivity = Subactivity::factory()->hasAttached($activity)->name('abc')->create();
+        Subactivity::factory()->hasAttached($activity)->name('def')->create();
+
+        $response = $this->patchJson(route('api.subactivity.update', ['subactivity' => $subactivity->id]), [
+            'name' => 'def',
+            'activities' => [$activity->id],
+            'is_filterable' => false,
+        ]);
+
+        $response->assertJsonValidationErrors(['name' => 'Name ist bereits vergeben']);
+    }
+
+    public function testItCanSetAnotherActivity(): void
+    {
+        $this->login()->loginNami();
+        $activity = Activity::factory()->create();
+        $newActivity = Activity::factory()->create();
+        $subactivity = Subactivity::factory()->hasAttached($activity)->create();
+
+        $response = $this->patchJson(route('api.subactivity.update', ['subactivity' => $subactivity->id]), [
+            'name' => 'abc',
+            'activities' => [$activity->id, $newActivity->id],
+            'is_filterable' => false,
+        ]);
+
+        $this->assertDatabaseHas('activity_subactivity', ['activity_id' => $activity->id, 'subactivity_id' => $subactivity->id]);
+        $this->assertDatabaseHas('activity_subactivity', ['activity_id' => $newActivity->id, 'subactivity_id' => $subactivity->id]);
+    }
+
+    public function testItCannotSetAnotherNamiActivity(): void
+    {
+        $this->login()->loginNami();
+        $activity = Activity::factory()->create();
+        $newActivity = Activity::factory()->inNami(556)->create();
+        $subactivity = Subactivity::factory()->hasAttached($activity)->name('abc')->inNami(667)->create();
+
+        $response = $this->patchJson(route('api.subactivity.update', ['subactivity' => $subactivity->id]), [
+            'name' => 'abc',
+            'activities' => [$activity->id, $newActivity->id],
+            'is_filterable' => false,
+        ]);
+
+        $response->assertJsonValidationErrors(['activities' => 'Tätigkeit kann nicht hinzugefügt werden.']);
+    }
+
+    public function testItCannotRemoveANamiActivity(): void
+    {
+        $this->login()->loginNami();
+        $activity = Activity::factory()->create();
+        $newActivity = Activity::factory()->inNami(556)->create();
+        $subactivity = Subactivity::factory()->hasAttached($activity)->hasAttached($newActivity)->name('abc')->inNami(667)->create();
+
+        $response = $this->patchJson(route('api.subactivity.update', ['subactivity' => $subactivity->id]), [
+            'name' => 'abc',
+            'activities' => [$activity->id],
+            'is_filterable' => false,
+        ]);
+
+        $response->assertJsonValidationErrors(['activities' => 'Tätigkeit kann nicht entfernt werden.']);
+    }
+
+    public function testItCannotRemoveActivityIfMembershipsHasMembers(): void
+    {
+        $this->login()->loginNami();
+        $activity = Activity::factory()->create();
+        $newActivity = Activity::factory()->create();
+        $subactivity = Subactivity::factory()->hasAttached($activity)->create();
+        Member::factory()->defaults()->has(Membership::factory()->for($activity)->for($subactivity))->create();
+
+        $response = $this->patchJson(route('api.subactivity.update', ['subactivity' => $subactivity->id]), [
+            'name' => 'abc',
+            'activities' => [$newActivity->id],
+            'is_filterable' => false,
+        ]);
+
+        $response->assertJsonValidationErrors(['activities' => 'Tätigkeit hat noch Mitglieder.']);
+    }
+
+    public function testItCannotSetNoActivity(): void
+    {
+        $this->login()->loginNami();
+        $activity = Activity::factory()->create();
+        $subactivity = Subactivity::factory()->hasAttached($activity)->create();
+
+        $response = $this->patchJson(route('api.subactivity.update', ['subactivity' => $subactivity->id]), [
+            'name' => 'abc',
+            'activities' => [],
+            'is_filterable' => false,
+        ]);
+
+        $response->assertJsonValidationErrors(['activities' => 'Tätigkeiten muss mindestens 1 Elemente haben.']);
+    }
 }
diff --git a/tests/Feature/Activity/UpdateTest.php b/tests/Feature/Activity/UpdateTest.php
index 75eba9be..cce95b1a 100644
--- a/tests/Feature/Activity/UpdateTest.php
+++ b/tests/Feature/Activity/UpdateTest.php
@@ -3,6 +3,8 @@
 namespace Tests\Feature\Activity;
 
 use App\Activity;
+use App\Member\Member;
+use App\Member\Membership;
 use App\Subactivity;
 use Illuminate\Foundation\Testing\DatabaseTransactions;
 use Tests\TestCase;
@@ -158,4 +160,21 @@ class UpdateTest extends TestCase
 
         $this->assertDatabaseEmpty('activity_subactivity');
     }
+
+    public function testItCannotSetSubactivityIfItStillHasMembers(): void
+    {
+        $this->login()->loginNami();
+        $activity = Activity::factory()->create();
+        $subactivity = Subactivity::factory()->hasAttached($activity)->create();
+        $newSubactivity = Subactivity::factory()->create();
+        Member::factory()->defaults()->has(Membership::factory()->for($activity)->for($subactivity))->create();
+
+        $response = $this->patch(route('activity.update', ['activity' => $activity]), [
+            'name' => 'abc',
+            'is_filterable' => false,
+            'subactivities' => [$newSubactivity->id],
+        ]);
+
+        $response->assertSessionHasErrors(['subactivities' => 'Untergliederung hat noch Mitglieder.']);
+    }
 }