diff --git a/packages/backend/src/core/CustomEmojiService.ts b/packages/backend/src/core/CustomEmojiService.ts
index 9661a0aea3..d438820e27 100644
--- a/packages/backend/src/core/CustomEmojiService.ts
+++ b/packages/backend/src/core/CustomEmojiService.ts
@@ -379,6 +379,13 @@ export class CustomEmojiService implements OnApplicationShutdown {
 			this.cache.set(`${emoji.name} ${emoji.host}`, emoji);
 		}
 	}
+	/**
+	 * ローカル内の絵文字に重複がないかチェックします
+	 * @param name 絵文字名
+	 */
+	public async isDuplicateCheck(name: string): Promise<boolean> {
+		return (await this.emojisRepository.findOneBy({ name, host: IsNull() })) !== null;
+	}
 
 	@bindThis
 	public dispose(): void {
diff --git a/packages/backend/src/server/api/endpoints/admin/emoji/add.ts b/packages/backend/src/server/api/endpoints/admin/emoji/add.ts
index 24d3a8a943..1b9dc1c2ae 100644
--- a/packages/backend/src/server/api/endpoints/admin/emoji/add.ts
+++ b/packages/backend/src/server/api/endpoints/admin/emoji/add.ts
@@ -23,6 +23,11 @@ export const meta = {
 			code: 'NO_SUCH_FILE',
 			id: 'fc46b5a4-6b92-4c33-ac66-b806659bb5cf',
 		},
+		duplicateName: {
+			message: 'Duplicate name.',
+			code: 'DUPLICATE_NAME',
+			id: 'f7a3462c-4e6e-4069-8421-b9bd4f4c3975',
+		},
 	},
 } as const;
 
@@ -64,7 +69,8 @@ export default class extends Endpoint<typeof meta, typeof paramDef> { // eslint-
 		super(meta, paramDef, async (ps, me) => {
 			const driveFile = await this.driveFilesRepository.findOneBy({ id: ps.fileId });
 			if (driveFile == null) throw new ApiError(meta.errors.noSuchFile);
-
+			const duplicateCheck = await this.customEmojiService.isDuplicateCheck(ps.name);
+			if (duplicateCheck != null) throw new ApiError(meta.errors.duplicateName);
 			const emoji = await this.customEmojiService.add({
 				driveFile,
 				name: ps.name,
diff --git a/packages/backend/src/server/api/endpoints/admin/emoji/update.ts b/packages/backend/src/server/api/endpoints/admin/emoji/update.ts
index 2d69857408..c057eeb590 100644
--- a/packages/backend/src/server/api/endpoints/admin/emoji/update.ts
+++ b/packages/backend/src/server/api/endpoints/admin/emoji/update.ts
@@ -74,6 +74,10 @@ export default class extends Endpoint<typeof meta, typeof paramDef> { // eslint-
 				driveFile = await this.driveFilesRepository.findOneBy({ id: ps.fileId });
 				if (driveFile == null) throw new ApiError(meta.errors.noSuchFile);
 			}
+			if (ps.name) {
+				const duplicateCheck = await this.customEmojiService.isDuplicateCheck(ps.name);
+				if (duplicateCheck != null) throw new ApiError(meta.errors.sameNameEmojiExists);
+			}
 
 			await this.customEmojiService.update(ps.id, {
 				driveFile,