The existence of malicious users could damage the correctness and availability of the peer-to-peer (P2P) e-commerce systems. Reputation-Based trust mechanisms can recognize these malicious peers by computing the trustworthiness of the peers. The validity of a reputation-based trust mechanism relies on some well-chosen trust factors,which directly influence the computation of trust value,the accuracy of the trust mechanism,and the resistibility of the trust mechanism to various attacks. However,there are some problems in the above three aspects of existing reputation-based trust mechanisms in P2P environments,such as the selection of trust factors. This paper presents a novel reputation-based trust mechanism for P2P e-commerce systems. In this mechanism,a peer has two kinds of reputations,namely local reputations and global reputations. The local reputation of a peer relative to another peer is calculated in terms of the reference peer’s rating of the transaction between the two peers,whereas the global reputation is computed based on all peers’ rating of the transaction between them. To compute the local and global reputations precisely and to obtain stronger resistibility to attacks as well,many comprehensive factors in computing trust value are introduced in the mechanism. To estimate the validity of the rating given by peers,a quality model and a computational method are also employed to evaluate the objectivity and the credibility of the rating,respectively. To compute the trust value of a peer,the concept of belief factor is introduced to integrate the local reputation with the global reputation. Furthermore,a method is put forward in this paper for determining belief factor. Finally,the effectiveness and resistibility of the proposed trust mechanism are analyzed theoretically and evaluated experimentally. The experimental results show that the proposed trust mechanism outperforms existing mechanisms,and can effectively be applied to the P2P e-commerce system.