Ji et al improved R.Revest?s PayWord protocol based on hash chains and proposed a micropayment protocol which had better features on security and fairness, but it did not solve the problems of malicious overdraft and timeliness. Furthermore its efficiency and security was restricted by the inherent shortcoming of conventional hash chains. The paper proposes an authentication protocol for M-commerce based on Self- Updating Hash Chains scheme, and designs a micropayment protocol. The protocols fit scenario of micropayment such as information commodity between a mobile user and a fixed service provider. The analyses show that the proposed authentication protocol needs fewer messages to authenticate mobile user in the foremost time, session keys are negotiated efficiently, as well as fine-authentication is realized. The proposed protocols do not only solve the problems existed in Ji?s protocol, but also have better features on security, efficiency and fairness.