diff --git a/x-pack/plugins/cases/common/api/cases/comment/index.test.ts b/x-pack/plugins/cases/common/api/cases/comment/index.test.ts
index ab27b976a5f71..23ea839c5d540 100644
--- a/x-pack/plugins/cases/common/api/cases/comment/index.test.ts
+++ b/x-pack/plugins/cases/common/api/cases/comment/index.test.ts
@@ -31,7 +31,7 @@ import {
   BulkGetAttachmentsRequestRt,
   BulkGetAttachmentsResponseRt,
 } from '.';
-import { MAX_COMMENT_LENGTH } from '../../../constants';
+import { MAX_COMMENT_LENGTH, MAX_BULK_CREATE_ATTACHMENTS } from '../../../constants';
 
 describe('Comments', () => {
   describe('CommentAttributesBasicRt', () => {
@@ -843,6 +843,27 @@ describe('Comments', () => {
         right: defaultRequest,
       });
     });
+
+    describe('errors', () => {
+      it(`throws error when attachments are more than ${MAX_BULK_CREATE_ATTACHMENTS}`, () => {
+        const comment = {
+          comment: 'Solve this fast!',
+          type: CommentType.user,
+          owner: 'cases',
+        };
+        const attachments = Array(MAX_BULK_CREATE_ATTACHMENTS + 1).fill(comment);
+
+        expect(PathReporter.report(BulkCreateCommentRequestRt.decode(attachments))).toContain(
+          `The length of the field attachments is too long. Array must be of length <= ${MAX_BULK_CREATE_ATTACHMENTS}.`
+        );
+      });
+
+      it(`no errors when empty array of attachments`, () => {
+        expect(PathReporter.report(BulkCreateCommentRequestRt.decode([]))).toStrictEqual([
+          'No errors!',
+        ]);
+      });
+    });
   });
 
   describe('BulkGetAttachmentsRequestRt', () => {
diff --git a/x-pack/plugins/cases/common/api/cases/comment/index.ts b/x-pack/plugins/cases/common/api/cases/comment/index.ts
index 50b93a8c70461..f23d0f82377be 100644
--- a/x-pack/plugins/cases/common/api/cases/comment/index.ts
+++ b/x-pack/plugins/cases/common/api/cases/comment/index.ts
@@ -10,6 +10,7 @@ import {
   MAX_BULK_GET_ATTACHMENTS,
   MAX_COMMENTS_PER_PAGE,
   MAX_COMMENT_LENGTH,
+  MAX_BULK_CREATE_ATTACHMENTS,
 } from '../../../constants';
 import { limitedArraySchema, paginationSchema, limitedStringSchema } from '../../../schema';
 import { jsonValueRt } from '../../runtime_types';
@@ -328,7 +329,12 @@ export const FindCommentsQueryParamsRt = rt.intersection([
   paginationSchema({ maxPerPage: MAX_COMMENTS_PER_PAGE }),
 ]);
 
-export const BulkCreateCommentRequestRt = rt.array(CommentRequestRt);
+export const BulkCreateCommentRequestRt = limitedArraySchema({
+  codec: CommentRequestRt,
+  min: 0,
+  max: MAX_BULK_CREATE_ATTACHMENTS,
+  fieldName: 'attachments',
+});
 
 export const BulkGetAttachmentsRequestRt = rt.strict({
   ids: limitedArraySchema({
diff --git a/x-pack/plugins/cases/common/constants/index.ts b/x-pack/plugins/cases/common/constants/index.ts
index 540be4c149f2b..5e09a6bb1db30 100644
--- a/x-pack/plugins/cases/common/constants/index.ts
+++ b/x-pack/plugins/cases/common/constants/index.ts
@@ -125,6 +125,7 @@ export const MAX_LENGTH_PER_TAG = 256 as const;
 export const MAX_TAGS_PER_CASE = 200 as const;
 export const MAX_DELETE_IDS_LENGTH = 100 as const;
 export const MAX_CASES_TO_UPDATE = 100 as const;
+export const MAX_BULK_CREATE_ATTACHMENTS = 100 as const;
 
 /**
  * Cases features
diff --git a/x-pack/plugins/cases/server/client/attachments/bulk_create.test.ts b/x-pack/plugins/cases/server/client/attachments/bulk_create.test.ts
index d9cb3d9ea190b..5d72eb17277b0 100644
--- a/x-pack/plugins/cases/server/client/attachments/bulk_create.test.ts
+++ b/x-pack/plugins/cases/server/client/attachments/bulk_create.test.ts
@@ -7,7 +7,7 @@
 
 import { comment, actionComment } from '../../mocks';
 import { createCasesClientMockArgs } from '../mocks';
-import { MAX_COMMENT_LENGTH } from '../../../common/constants';
+import { MAX_COMMENT_LENGTH, MAX_BULK_CREATE_ATTACHMENTS } from '../../../common/constants';
 import { bulkCreate } from './bulk_create';
 
 describe('bulkCreate', () => {
@@ -24,6 +24,14 @@ describe('bulkCreate', () => {
     ).rejects.toThrow('invalid keys "foo"');
   });
 
+  it(`throws error when attachments are more than ${MAX_BULK_CREATE_ATTACHMENTS}`, async () => {
+    const attachments = Array(MAX_BULK_CREATE_ATTACHMENTS + 1).fill(comment);
+
+    await expect(bulkCreate({ attachments, caseId: 'test-case' }, clientArgs)).rejects.toThrow(
+      `The length of the field attachments is too long. Array must be of length <= ${MAX_BULK_CREATE_ATTACHMENTS}.`
+    );
+  });
+
   describe('comments', () => {
     it('should throw an error if the comment length is too long', async () => {
       const longComment = Array(MAX_COMMENT_LENGTH + 1)
diff --git a/x-pack/test/cases_api_integration/security_and_spaces/tests/common/internal/bulk_create_attachments.ts b/x-pack/test/cases_api_integration/security_and_spaces/tests/common/internal/bulk_create_attachments.ts
index 0df7e207081a0..a0b626482f473 100644
--- a/x-pack/test/cases_api_integration/security_and_spaces/tests/common/internal/bulk_create_attachments.ts
+++ b/x-pack/test/cases_api_integration/security_and_spaces/tests/common/internal/bulk_create_attachments.ts
@@ -218,17 +218,6 @@ export default ({ getService }: FtrProviderContext): void => {
           });
         });
 
-        it('should bulk create 100 file attachments when there is another attachment type in the request', async () => {
-          const fileRequests = [...Array(100).keys()].map(() => getFilesAttachmentReq());
-
-          const postedCase = await createCase(supertest, postCaseReq);
-          await bulkCreateAttachments({
-            supertest,
-            caseId: postedCase.id,
-            params: [postExternalReferenceSOReq, ...fileRequests],
-          });
-        });
-
         it('should bulk create 99 file attachments when the case has a file associated to it', async () => {
           const postedCase = await createCase(
             supertestWithoutAuth,
@@ -376,6 +365,23 @@ export default ({ getService }: FtrProviderContext): void => {
         });
       });
 
+      it('400s when attempting to add more than 100 attachments', async () => {
+        const comment = {
+          type: CommentType.user,
+          comment: 'test',
+          owner: 'securitySolutionFixture',
+        };
+
+        const attachments = Array(101).fill(comment);
+
+        await bulkCreateAttachments({
+          supertest,
+          caseId: 'test-case-id',
+          params: attachments,
+          expectedHttpCode: 400,
+        });
+      });
+
       it('400s when attempting to create a comment with a different owner than the case', async () => {
         const postedCase = await createCase(
           supertest,