Abstract: Mobile agent systems are identified as a programming paradigm that allows flexible structuring of distributed computation over the Internet. It is expected that they will play an important role in the future information society and especially in e-commerce applications. Despite their benefits, their adoption is largely hampered by the new security issues they raise. In this paper, by using verifiable secret sharing scheme and the theory of cross validation, an optimistic payment protocol based on mobile agents is proposed. This protocol can protect the confidentiality of sensitive payment information carried by mobile agents from being spied by malicious hosts, and mobile agent can verify that the product which he is about to receive is the one he is paying for without exposing it. Moreover, the trusted third party is offline unless someone is misbehaving or prematurely aborting.