There are recently several studies of online auctions which have focused on exploring a bidder's bidding behavior in IS area. Those studies, however, have been limited to account for bidders' bidding behavior in the view of TAM and trust, not considering perceived price fairness and competition intensity. Although this view point seems reasonable in the online auction sites, few previous studies employing this perspective are found in the relevant literatures. Based on it, this study developed a comprehensive model based on trust and TAM in terms of perceived price fairness to explain competition intensity in the online auction sites. This study collected 269 survey responses from online bidders who have prior experiences with online auction sites. The survey data are used to empirically verify 11 research hypothesis by using LISREL. The results indicate that trust in websites, trust in sellers and perceived usefulness have significant impacts on perceived price fairness. Finally, perceived price fairness is strongly related to competition intensity in the online auction. This study ends with theoretical and managerial implications, as well as limitations and future research.