Face recognition is a computer technique to capture the feature of the human face for user authentication. In the advanced mobile technology, mobile devices take the place of computers to become the major human-computer interaction. Related researches become more and more popular. This study discusses about the identification of users on the mobile devices. Recently, many users still use passwords for user authentication. However, such traditional password identification may not be secure since the passwords are easily intercepted. To solve this problem, this thesis adopts facial recognition for screen unlocking on the mobile devices.