diff --git a/apps/api/src/modules/inquiries/application/__tests__/create-inquiry.handler.spec.ts b/apps/api/src/modules/inquiries/application/__tests__/create-inquiry.handler.spec.ts
index 88d5204..3de41fd 100644
--- a/apps/api/src/modules/inquiries/application/__tests__/create-inquiry.handler.spec.ts
+++ b/apps/api/src/modules/inquiries/application/__tests__/create-inquiry.handler.spec.ts
@@ -2,6 +2,7 @@ import type { EventBus } from '@nestjs/cqrs';
 import type { IInquiryRepository } from '../../domain/repositories/inquiry.repository';
 import { CreateInquiryCommand } from '../commands/create-inquiry/create-inquiry.command';
 import { CreateInquiryHandler } from '../commands/create-inquiry/create-inquiry.handler';
+import { SanitizeHtmlService } from '../services/sanitize-html.service';
 
 describe('CreateInquiryHandler', () => {
   let handler: CreateInquiryHandler;
@@ -10,6 +11,7 @@ describe('CreateInquiryHandler', () => {
   let mockPrisma: {
     listing: { findUnique: ReturnType<typeof vi.fn> };
   };
+  let sanitizer: SanitizeHtmlService;
 
   beforeEach(() => {
     mockInquiryRepo = {
@@ -29,11 +31,14 @@ describe('CreateInquiryHandler', () => {
 
     const mockLogger = { log: vi.fn(), warn: vi.fn(), error: vi.fn(), debug: vi.fn(), verbose: vi.fn() };
 
+    sanitizer = new SanitizeHtmlService();
+
     handler = new CreateInquiryHandler(
       mockInquiryRepo as any,
       mockEventBus as unknown as EventBus,
       mockPrisma as any,
       mockLogger as any,
+      sanitizer,
     );
   });
 
@@ -95,4 +100,48 @@ describe('CreateInquiryHandler', () => {
       }),
     );
   });
+
+  it('sanitizes <script> and on* handlers before persisting', async () => {
+    mockPrisma.listing.findUnique.mockResolvedValue({ id: 'listing-1' });
+    mockInquiryRepo.save.mockResolvedValue(undefined);
+
+    const command = new CreateInquiryCommand(
+      'user-1',
+      'listing-1',
+      '<p>Chào anh</p><script>alert(1)</script><img src=x onerror="alert(2)"/>',
+      null,
+    );
+
+    await handler.execute(command);
+
+    const savedInquiry = mockInquiryRepo.save.mock.calls[0][0];
+    const persisted: string = savedInquiry.message;
+
+    expect(persisted).toContain('<p>Chào anh</p>');
+    expect(persisted).not.toContain('<script');
+    expect(persisted).not.toContain('alert(1)');
+    expect(persisted).not.toContain('onerror');
+    expect(persisted).not.toContain('<img');
+  });
+
+  it('forces rel/target on anchor tags and drops javascript: URLs', async () => {
+    mockPrisma.listing.findUnique.mockResolvedValue({ id: 'listing-1' });
+    mockInquiryRepo.save.mockResolvedValue(undefined);
+
+    const command = new CreateInquiryCommand(
+      'user-1',
+      'listing-1',
+      '<a href="https://example.com">ok</a><a href="javascript:alert(1)">bad</a>',
+      null,
+    );
+
+    await handler.execute(command);
+
+    const persisted: string = mockInquiryRepo.save.mock.calls[0][0].message;
+
+    expect(persisted).toContain('href="https://example.com"');
+    expect(persisted).toContain('rel="noopener noreferrer nofollow"');
+    expect(persisted).toContain('target="_blank"');
+    expect(persisted).not.toContain('javascript:');
+  });
 });
diff --git a/apps/api/src/modules/inquiries/application/__tests__/sanitize-html.service.spec.ts b/apps/api/src/modules/inquiries/application/__tests__/sanitize-html.service.spec.ts
new file mode 100644
index 0000000..d09bfc1
--- /dev/null
+++ b/apps/api/src/modules/inquiries/application/__tests__/sanitize-html.service.spec.ts
@@ -0,0 +1,47 @@
+import { SanitizeHtmlService } from '../services/sanitize-html.service';
+
+describe('SanitizeHtmlService', () => {
+  const sanitizer = new SanitizeHtmlService();
+
+  it('strips <script> tags', () => {
+    const out = sanitizer.sanitizeInquiryMessage('<p>Hi</p><script>alert(1)</script>');
+    expect(out).toBe('<p>Hi</p>');
+  });
+
+  it('drops inline event handlers like onerror', () => {
+    const out = sanitizer.sanitizeInquiryMessage('<img src=x onerror="alert(1)" />');
+    expect(out).not.toContain('onerror');
+    expect(out).not.toContain('<img');
+  });
+
+  it('keeps allow-listed inline tags', () => {
+    const out = sanitizer.sanitizeInquiryMessage('<b>bold</b> <i>italic</i><br/><p>para</p>');
+    expect(out).toContain('<b>bold</b>');
+    expect(out).toContain('<i>italic</i>');
+    expect(out).toContain('<br />');
+    expect(out).toContain('<p>para</p>');
+  });
+
+  it('forces rel and target on <a>', () => {
+    const out = sanitizer.sanitizeInquiryMessage('<a href="https://example.com">x</a>');
+    expect(out).toContain('href="https://example.com"');
+    expect(out).toContain('rel="noopener noreferrer nofollow"');
+    expect(out).toContain('target="_blank"');
+  });
+
+  it('drops javascript: scheme links', () => {
+    const out = sanitizer.sanitizeInquiryMessage('<a href="javascript:alert(1)">x</a>');
+    expect(out).not.toContain('javascript:');
+  });
+
+  it('returns empty string for nullish input', () => {
+    expect(sanitizer.sanitizeInquiryMessage(null)).toBe('');
+    expect(sanitizer.sanitizeInquiryMessage(undefined)).toBe('');
+    expect(sanitizer.sanitizeInquiryMessage('')).toBe('');
+  });
+
+  it('preserves plain Vietnamese text', () => {
+    const text = 'Tôi muốn xem nhà vào cuối tuần này, anh sắp xếp giúp ạ.';
+    expect(sanitizer.sanitizeInquiryMessage(text)).toBe(text);
+  });
+});
diff --git a/apps/api/src/modules/inquiries/application/commands/create-inquiry/create-inquiry.handler.ts b/apps/api/src/modules/inquiries/application/commands/create-inquiry/create-inquiry.handler.ts
index 4bf92c1..645d103 100644
--- a/apps/api/src/modules/inquiries/application/commands/create-inquiry/create-inquiry.handler.ts
+++ b/apps/api/src/modules/inquiries/application/commands/create-inquiry/create-inquiry.handler.ts
@@ -4,6 +4,7 @@ import { createId } from '@paralleldrive/cuid2';
 import { DomainException, NotFoundException, PrismaService, LoggerService } from '@modules/shared';
 import { InquiryEntity } from '../../../domain/entities/inquiry.entity';
 import { INQUIRY_REPOSITORY, type IInquiryRepository } from '../../../domain/repositories/inquiry.repository';
+import { SanitizeHtmlService } from '../../services/sanitize-html.service';
 import { CreateInquiryCommand } from './create-inquiry.command';
 
 export interface CreateInquiryResult {
@@ -19,6 +20,7 @@ export class CreateInquiryHandler implements ICommandHandler<CreateInquiryComman
     private readonly eventBus: EventBus,
     private readonly prisma: PrismaService,
     private readonly logger: LoggerService,
+    private readonly sanitizer: SanitizeHtmlService,
   ) {}
 
   async execute(command: CreateInquiryCommand): Promise<CreateInquiryResult> {
@@ -33,11 +35,12 @@ export class CreateInquiryHandler implements ICommandHandler<CreateInquiryComman
       }
 
       const id = createId();
+      const sanitizedMessage = this.sanitizer.sanitizeInquiryMessage(command.message);
       const inquiry = InquiryEntity.createNew(
         id,
         command.listingId,
         command.userId,
-        command.message,
+        sanitizedMessage,
         command.phone,
       );
 
diff --git a/apps/api/src/modules/inquiries/application/services/sanitize-html.service.ts b/apps/api/src/modules/inquiries/application/services/sanitize-html.service.ts
new file mode 100644
index 0000000..05dcea6
--- /dev/null
+++ b/apps/api/src/modules/inquiries/application/services/sanitize-html.service.ts
@@ -0,0 +1,52 @@
+import { Injectable } from '@nestjs/common';
+import sanitizeHtml from 'sanitize-html';
+
+/**
+ * Whitelist-based HTML sanitizer for inquiry messages.
+ *
+ * Defense-in-depth complement to the global SanitizeInputMiddleware:
+ * - the global middleware strips ALL tags from incoming HTTP request bodies,
+ * - this service runs at the application layer right before persistence,
+ *   guaranteeing safe content even if a future code path (queue replay,
+ *   internal command dispatch, import job) bypasses the HTTP middleware.
+ *
+ * Allow-list is intentionally minimal per TEC-2929:
+ *   <b>, <i>, <br>, <p>, <a> (links forced to rel=noopener noreferrer nofollow,
+ *   target=_blank, http(s) only).
+ *
+ * Everything else (including <script>, <iframe>, <img onerror=...>, inline
+ * event handlers, javascript: URLs, etc.) is dropped.
+ */
+@Injectable()
+export class SanitizeHtmlService {
+  private static readonly OPTIONS: sanitizeHtml.IOptions = {
+    allowedTags: ['b', 'i', 'br', 'p', 'a'],
+    allowedAttributes: {
+      a: ['href', 'rel', 'target'],
+    },
+    allowedSchemes: ['http', 'https', 'mailto', 'tel'],
+    allowedSchemesAppliedToAttributes: ['href'],
+    allowProtocolRelative: false,
+    disallowedTagsMode: 'discard',
+    transformTags: {
+      a: sanitizeHtml.simpleTransform('a', {
+        rel: 'noopener noreferrer nofollow',
+        target: '_blank',
+      }),
+    },
+  };
+
+  /**
+   * Sanitize a single string of inquiry message content.
+   *
+   * Returns the sanitized string. Always returns a string (never throws on
+   * non-string input — empty string is returned for null/undefined to keep
+   * call sites simple).
+   */
+  sanitizeInquiryMessage(input: string | null | undefined): string {
+    if (typeof input !== 'string' || input.length === 0) {
+      return '';
+    }
+    return sanitizeHtml(input, SanitizeHtmlService.OPTIONS);
+  }
+}
diff --git a/apps/api/src/modules/inquiries/inquiries.module.ts b/apps/api/src/modules/inquiries/inquiries.module.ts
index b10bc76..287b206 100644
--- a/apps/api/src/modules/inquiries/inquiries.module.ts
+++ b/apps/api/src/modules/inquiries/inquiries.module.ts
@@ -4,6 +4,7 @@ import { CreateInquiryHandler } from './application/commands/create-inquiry/crea
 import { MarkInquiryReadHandler } from './application/commands/mark-inquiry-read/mark-inquiry-read.handler';
 import { GetInquiriesByAgentHandler } from './application/queries/get-inquiries-by-agent/get-inquiries-by-agent.handler';
 import { GetInquiriesByListingHandler } from './application/queries/get-inquiries-by-listing/get-inquiries-by-listing.handler';
+import { SanitizeHtmlService } from './application/services/sanitize-html.service';
 import { INQUIRY_REPOSITORY } from './domain/repositories/inquiry.repository';
 import { PrismaInquiryRepository } from './infrastructure/repositories/prisma-inquiry.repository';
 import { InquiriesController } from './presentation/controllers/inquiries.controller';
@@ -20,6 +21,7 @@ const QueryHandlers = [
   controllers: [InquiriesController],
   providers: [
     { provide: INQUIRY_REPOSITORY, useClass: PrismaInquiryRepository },
+    SanitizeHtmlService,
     ...CommandHandlers,
     ...QueryHandlers,
   ],