diff --git a/packages/backend/src/core/UserBlockingService.ts b/packages/backend/src/core/UserBlockingService.ts
index 2f1310b8efe7..b143a1ba4318 100644
--- a/packages/backend/src/core/UserBlockingService.ts
+++ b/packages/backend/src/core/UserBlockingService.ts
@@ -20,6 +20,7 @@ import { UserWebhookService } from '@/core/UserWebhookService.js';
 import { bindThis } from '@/decorators.js';
 import { CacheService } from '@/core/CacheService.js';
 import { UserFollowingService } from '@/core/UserFollowingService.js';
+import { RoleService } from '@/core/RoleService.js';
 
 @Injectable()
 export class UserBlockingService implements OnModuleInit {
@@ -49,6 +50,7 @@ export class UserBlockingService implements OnModuleInit {
 		private webhookService: UserWebhookService,
 		private apRendererService: ApRendererService,
 		private loggerService: LoggerService,
+		private roleService: RoleService,
 	) {
 		this.logger = this.loggerService.getLogger('user-block');
 	}
@@ -58,7 +60,11 @@ export class UserBlockingService implements OnModuleInit {
 	}
 
 	@bindThis
-	public async block(blocker: MiUser, blockee: MiUser, silent = false) {
+	public async block(blocker: MiUser, blockee: MiUser, silent = false): Promise<
+		| null
+		| 'BLOCKEE_IS_MODERATOR'
+	> {
+		if (await this.roleService.isModerator(blockee)) return 'BLOCKEE_IS_MODERATOR';
 		await Promise.all([
 			this.cancelRequest(blocker, blockee, silent),
 			this.cancelRequest(blockee, blocker, silent),
@@ -89,6 +95,8 @@ export class UserBlockingService implements OnModuleInit {
 			const content = this.apRendererService.addContext(this.apRendererService.renderBlock(blocking));
 			this.queueService.deliver(blocker, content, blockee.inbox, false);
 		}
+
+		return null;
 	}
 
 	@bindThis
diff --git a/packages/backend/src/core/activitypub/ApInboxService.ts b/packages/backend/src/core/activitypub/ApInboxService.ts
index e2164fec1d93..d23f8f0fdd37 100644
--- a/packages/backend/src/core/activitypub/ApInboxService.ts
+++ b/packages/backend/src/core/activitypub/ApInboxService.ts
@@ -357,8 +357,11 @@ export class ApInboxService {
 			return 'skip: ブロックしようとしているユーザーはローカルユーザーではありません';
 		}
 
-		await this.userBlockingService.block(await this.usersRepository.findOneByOrFail({ id: actor.id }), await this.usersRepository.findOneByOrFail({ id: blockee.id }));
-		return 'ok';
+		const error = await this.userBlockingService.block(await this.usersRepository.findOneByOrFail({ id: actor.id }), await this.usersRepository.findOneByOrFail({ id: blockee.id }));
+		switch (error) {
+			case null: return 'ok';
+			case 'BLOCKEE_IS_MODERATOR': return 'skip: Blocking Moderator is not allowed.';
+		}
 	}
 
 	@bindThis
diff --git a/packages/backend/src/queue/processors/RelationshipProcessorService.ts b/packages/backend/src/queue/processors/RelationshipProcessorService.ts
index 408b02fb380c..9bf586b36598 100644
--- a/packages/backend/src/queue/processors/RelationshipProcessorService.ts
+++ b/packages/backend/src/queue/processors/RelationshipProcessorService.ts
@@ -61,8 +61,11 @@ export class RelationshipProcessorService {
 			this.usersRepository.findOneByOrFail({ id: job.data.from.id }),
 			this.usersRepository.findOneByOrFail({ id: job.data.to.id }),
 		]);
-		await this.userBlockingService.block(blockee, blocker, job.data.silent);
-		return 'ok';
+		const error = await this.userBlockingService.block(blockee, blocker, job.data.silent);
+		switch (error) {
+			case null: return 'ok';
+			case 'BLOCKEE_IS_MODERATOR': return 'skip: Blocking Moderator is not allowed.';
+		}
 	}
 
 	@bindThis
diff --git a/packages/backend/src/server/api/endpoints/blocking/create.ts b/packages/backend/src/server/api/endpoints/blocking/create.ts
index 506621574969..b7681c068ad2 100644
--- a/packages/backend/src/server/api/endpoints/blocking/create.ts
+++ b/packages/backend/src/server/api/endpoints/blocking/create.ts
@@ -43,6 +43,12 @@ export const meta = {
 			code: 'ALREADY_BLOCKING',
 			id: '787fed64-acb9-464a-82eb-afbd745b9614',
 		},
+
+		blockeeIsModerator: {
+			message: 'Blocking Moderator is not allowed.',
+			code: 'BLOCKEE_IS_MODERATOR',
+			id: '3dca06d1-5ee8-4f14-aff1-917e9ba35e05',
+		},
 	},
 
 	res: {
@@ -99,11 +105,18 @@ export default class extends Endpoint<typeof meta, typeof paramDef> { // eslint-
 				throw new ApiError(meta.errors.alreadyBlocking);
 			}
 
-			await this.userBlockingService.block(blocker, blockee);
-
-			return await this.userEntityService.pack(blockee.id, blocker, {
-				schema: 'UserDetailedNotMe',
-			});
+			const error = await this.userBlockingService.block(blocker, blockee);
+
+			switch (error) {
+				case null: {
+					return await this.userEntityService.pack(blockee.id, blocker, {
+						schema: 'UserDetailedNotMe',
+					});
+				}
+				case 'BLOCKEE_IS_MODERATOR': throw new ApiError(meta.errors.blockeeIsModerator);
+				// 網羅性チェック
+				default: throw new Error(error satisfies never);
+			}
 		});
 	}
 }