diff --git a/Backend/src/controllers/CoursesInstructorController.ts b/Backend/src/controllers/CoursesInstructorController.ts
index 6ea2be56..746c2041 100644
--- a/Backend/src/controllers/CoursesInstructorController.ts
+++ b/Backend/src/controllers/CoursesInstructorController.ts
@@ -111,6 +111,29 @@ export class CoursesInstructorController {
         return await CoursesInstructorService.createCourse(value, decoded.id, thumbnail);
     }
 
+    /**
+     * อัปโหลดรูป thumbnail ของคอร์ส
+     * Upload course thumbnail image
+     * @param courseId - รหัสคอร์ส / Course ID
+     * @param file - ไฟล์รูปภาพ / Image file
+     */
+    @Post('{courseId}/thumbnail')
+    @Security('jwt', ['instructor'])
+    @SuccessResponse('200', 'Thumbnail uploaded successfully')
+    @Response('401', 'Invalid or expired token')
+    @Response('400', 'Validation error')
+    public async uploadThumbnail(
+        @Request() request: any,
+        @Path() courseId: number,
+        @UploadedFile() file: Express.Multer.File
+    ): Promise<{ code: number; message: string; data: { course_id: number; thumbnail_url: string } }> {
+        const token = request.headers.authorization?.replace('Bearer ', '');
+        if (!token) throw new ValidationError('No token provided');
+        if (!file.mimetype?.startsWith('image/')) throw new ValidationError('Only image files are allowed');
+
+        return await CoursesInstructorService.uploadThumbnail(token, courseId, file);
+    }
+
     /**
      * ลบคอร์ส (เฉพาะผู้สอนหลักเท่านั้น)
      * Delete a course (only primary instructor can delete)
diff --git a/Backend/src/services/CoursesInstructor.service.ts b/Backend/src/services/CoursesInstructor.service.ts
index 6e0d450b..8cb9838e 100644
--- a/Backend/src/services/CoursesInstructor.service.ts
+++ b/Backend/src/services/CoursesInstructor.service.ts
@@ -182,7 +182,7 @@ export class CoursesInstructorService {
 
     static async updateCourse(token: string, courseId: number, courseData: UpdateCourseInput): Promise<createCourseResponse> {
         try {
-            const courseInstructorId = await this.validateCourseInstructor(token, courseId);
+            await this.validateCourseInstructor(token, courseId);
 
             const course = await prisma.course.update({
                 where: {
@@ -191,23 +191,10 @@ export class CoursesInstructorService {
                 data: courseData
             });
 
-            // Generate presigned URL for thumbnail
-            let thumbnail_presigned_url: string | null = null;
-            if (course.thumbnail_url) {
-                try {
-                    thumbnail_presigned_url = await getPresignedUrl(course.thumbnail_url, 3600);
-                } catch (err) {
-                    logger.warn(`Failed to generate presigned URL for thumbnail: ${err}`);
-                }
-            }
-
             return {
                 code: 200,
                 message: 'Course updated successfully',
-                data: {
-                    ...course,
-                    thumbnail_url: thumbnail_presigned_url,
-                }
+                data: course
             };
         } catch (error) {
             logger.error('Failed to update course', { error });
@@ -215,6 +202,59 @@ export class CoursesInstructorService {
         }
     }
 
+    static async uploadThumbnail(token: string, courseId: number, file: Express.Multer.File): Promise<{ code: number; message: string; data: { course_id: number; thumbnail_url: string } }> {
+        try {
+            await this.validateCourseInstructor(token, courseId);
+
+            // Get current course to check for existing thumbnail
+            const currentCourse = await prisma.course.findUnique({
+                where: { id: courseId }
+            });
+
+            // Delete old thumbnail if exists
+            if (currentCourse?.thumbnail_url) {
+                try {
+                    await deleteFile(currentCourse.thumbnail_url);
+                    logger.info(`Deleted old thumbnail: ${currentCourse.thumbnail_url}`);
+                } catch (error) {
+                    logger.warn(`Failed to delete old thumbnail: ${error}`);
+                }
+            }
+
+            // Generate unique filename
+            const timestamp = Date.now();
+            const uniqueId = Math.random().toString(36).substring(2, 15);
+            const extension = file.originalname.split('.').pop() || 'jpg';
+            const safeFilename = `${timestamp}-${uniqueId}.${extension}`;
+            const filePath = `courses/${courseId}/thumbnail/${safeFilename}`;
+
+            // Upload to MinIO
+            await uploadFile(filePath, file.buffer, file.mimetype || 'image/jpeg');
+            logger.info(`Uploaded thumbnail: ${filePath}`);
+
+            // Update course with new thumbnail path
+            await prisma.course.update({
+                where: { id: courseId },
+                data: { thumbnail_url: filePath }
+            });
+
+            // Generate presigned URL for response
+            const presignedUrl = await getPresignedUrl(filePath, 3600);
+
+            return {
+                code: 200,
+                message: 'Thumbnail uploaded successfully',
+                data: {
+                    course_id: courseId,
+                    thumbnail_url: presignedUrl
+                }
+            };
+        } catch (error) {
+            logger.error('Failed to upload thumbnail', { error });
+            throw error;
+        }
+    }
+
     static async deleteCourse(token: string, courseId: number): Promise<createCourseResponse> {
         try {
             const courseInstructorId = await this.validateCourseInstructor(token, courseId);