With the progress of the mobile communication technology and the popularity of the handheld devices, mobile commerce is of great importance today. We can use these devices to conduct business, such as to purchase books, and stocks, and digital goods (videos, audios, codes), and to play games, receive email, and even access various network resources. When the requested services need to be verified, the authentication of users and the non-repudiation of transactions become very important. Completing these tasks in wireless environments is a challenge for mobile devices that have limited computational capabilities. In this paper, we propose a server-aided signature scheme based on secret sharing for mobile commerce. Through one-time password authentication and secret sharing technology, we generate the cooperative signature of the server and the handheld device to satisfy the issues of security, non-repudiation, simplicity, validity, and mobility.