diff --git a/.changeset/fresh-lies-breathe.md b/.changeset/fresh-lies-breathe.md
new file mode 100644
index 000000000..6ede40d19
--- /dev/null
+++ b/.changeset/fresh-lies-breathe.md
@@ -0,0 +1,6 @@
+---
+"@logto/shared": patch
+"@logto/core": patch
+---
+
+Add case sensitive username env variable
diff --git a/packages/core/src/queries/user.test.ts b/packages/core/src/queries/user.test.ts
index 81beaad58..ca1a5e941 100644
--- a/packages/core/src/queries/user.test.ts
+++ b/packages/core/src/queries/user.test.ts
@@ -1,8 +1,10 @@
 import { Users } from '@logto/schemas';
 import { convertToIdentifiers } from '@logto/shared';
+import Sinon from 'sinon';
 import { createMockPool, createMockQueryResult, sql } from 'slonik';
 
 import { mockUser } from '#src/__mocks__/index.js';
+import { EnvSet } from '#src/env-set/index.js';
 import { DeletionError } from '#src/errors/SlonikError/index.js';
 import type { QueryType } from '#src/utils/test-utils.js';
 import { expectSqlAssert } from '#src/utils/test-utils.js';
@@ -33,7 +35,17 @@ const {
   deleteUserIdentity,
 } = createUserQueries(pool);
 
+const stubIsCaseSensitiveUsername = (isCaseSensitiveUsername: boolean) =>
+  Sinon.stub(EnvSet, 'values').value({
+    ...EnvSet.values,
+    isCaseSensitiveUsername,
+  });
+
 describe('user query', () => {
+  beforeEach(() => {
+    stubIsCaseSensitiveUsername(true);
+  });
+
   const { table, fields } = convertToIdentifiers(Users);
   const databaseValue = {
     ...mockUser,
@@ -60,6 +72,24 @@ describe('user query', () => {
     await expect(findUserByUsername(mockUser.username!)).resolves.toEqual(databaseValue);
   });
 
+  it('findUserByUsername (case insensitive)', async () => {
+    stubIsCaseSensitiveUsername(false);
+    const expectSql = sql`
+      select ${sql.join(Object.values(fields), sql`,`)}
+      from ${table}
+      where lower(${fields.username})=lower($1)
+    `;
+
+    mockQuery.mockImplementationOnce(async (sql, values) => {
+      expectSqlAssert(sql, expectSql.sql);
+      expect(values).toEqual([mockUser.username]);
+
+      return createMockQueryResult([databaseValue]);
+    });
+
+    await expect(findUserByUsername(mockUser.username!)).resolves.toEqual(databaseValue);
+  });
+
   it('findUserByEmail', async () => {
     const expectSql = sql`
       select ${sql.join(Object.values(fields), sql`,`)}
@@ -132,6 +162,26 @@ describe('user query', () => {
     await expect(hasUser(mockUser.username!)).resolves.toEqual(true);
   });
 
+  it('hasUser (case insensitive)', async () => {
+    stubIsCaseSensitiveUsername(false);
+    const expectSql = sql`
+      SELECT EXISTS(
+        select ${fields.id}
+        from ${table}
+        where lower(${fields.username})=lower($1)
+      )
+    `;
+
+    mockQuery.mockImplementationOnce(async (sql, values) => {
+      expectSqlAssert(sql, expectSql.sql);
+      expect(values).toEqual([mockUser.username]);
+
+      return createMockQueryResult([{ exists: true }]);
+    });
+
+    await expect(hasUser(mockUser.username!)).resolves.toEqual(true);
+  });
+
   it('hasUserWithId', async () => {
     const expectSql = sql`
       SELECT EXISTS(
diff --git a/packages/core/src/queries/user.ts b/packages/core/src/queries/user.ts
index 72c3403c4..620095b36 100644
--- a/packages/core/src/queries/user.ts
+++ b/packages/core/src/queries/user.ts
@@ -7,6 +7,7 @@ import type { CommonQueryMethods } from 'slonik';
 import { sql } from 'slonik';
 
 import { buildUpdateWhereWithPool } from '#src/database/update-where.js';
+import { EnvSet } from '#src/env-set/index.js';
 import { DeletionError } from '#src/errors/SlonikError/index.js';
 import type { Search } from '#src/utils/search.js';
 import { buildConditionsFromSearch } from '#src/utils/search.js';
@@ -63,7 +64,11 @@ export const createUserQueries = (pool: CommonQueryMethods) => {
     pool.maybeOne<User>(sql`
       select ${sql.join(Object.values(fields), sql`,`)}
       from ${table}
-      where ${fields.username}=${username}
+      ${
+        EnvSet.values.isCaseSensitiveUsername
+          ? sql`where ${fields.username}=${username}`
+          : sql`where lower(${fields.username})=lower(${username})`
+      }
     `);
 
   const findUserByEmail = async (email: string) =>
@@ -100,7 +105,11 @@ export const createUserQueries = (pool: CommonQueryMethods) => {
     pool.exists(sql`
       select ${fields.id}
       from ${table}
-      where ${fields.username}=${username}
+      ${
+        EnvSet.values.isCaseSensitiveUsername
+          ? sql`where ${fields.username}=${username}`
+          : sql`where lower(${fields.username})=lower(${username})`
+      }
       ${conditionalSql(excludeUserId, (id) => sql`and ${fields.id}<>${id}`)}
     `);
 
diff --git a/packages/shared/src/node/env/GlobalValues.ts b/packages/shared/src/node/env/GlobalValues.ts
index 9e1f27bd6..34fa359e0 100644
--- a/packages/shared/src/node/env/GlobalValues.ts
+++ b/packages/shared/src/node/env/GlobalValues.ts
@@ -104,6 +104,9 @@ export default class GlobalValues {
   /** Maximum number of clients to keep in a single database pool (i.e. per `Tenant` class). */
   public readonly databasePoolSize = Number(getEnv('DATABASE_POOL_SIZE', '20'));
 
+  /** Case insensitive username */
+  public readonly isCaseSensitiveUsername = yes(getEnv('CASE_SENSITIVE_USERNAME', 'true'));
+
   /**
    * The Redis endpoint (optional). If it's set, the central cache mechanism will be automatically enabled.
    *