Abstract: With the enormous growth of the Internet and E-commerce, online trust has become an increasingly important issue. Over the Internet, players have to cope with much higher amount of uncertainty from quality of products and trustworthiness of participants. One way to address this uncertainty problem is to use feedback ratings about past behavior to help make recommendation and judgment on decision about who to trust. In this paper we introduce five basic trust parameters, and propose a computational trust model that combines these parameters to measure the trustworthiness of participants in online auctions. The simulation results show that compared to the current C2C trust model, the proposed model is more effective against malicious behavior.