diff --git a/.changeset/popular-chicken-share.md b/.changeset/popular-chicken-share.md
new file mode 100644
index 000000000..0a8968351
--- /dev/null
+++ b/.changeset/popular-chicken-share.md
@@ -0,0 +1,5 @@
+---
+"@logto/core": patch
+---
+
+fix a bug that prevents invitee from accepting the organization invitation if the email letter case is not matching
diff --git a/packages/core/src/libraries/organization-invitation.ts b/packages/core/src/libraries/organization-invitation.ts
index 17859be08..a89a8717f 100644
--- a/packages/core/src/libraries/organization-invitation.ts
+++ b/packages/core/src/libraries/organization-invitation.ts
@@ -157,7 +157,7 @@ export class OrganizationInvitationLibrary {
 
           const user = await userQueries.findUserById(acceptedUserId);
 
-          if (user.primaryEmail !== entity.invitee) {
+          if (user.primaryEmail?.toLowerCase() !== entity.invitee.toLowerCase()) {
             throw new RequestError({
               status: 422,
               code: 'request.invalid_input',