The focus of this paper is on a secure mobile commerce model based on wireless local area network (WLAN). The model is investigated through the accessing procedure, the roaming management procedure, and the electronic trade procedure. To solve the security problem in the WLAN, a novel authentication method is proposed, in which the mobile node (MN) is validated twice by an access point (AP) and a mobile agent (MA), and all the devices are authenticated in a register procedure with the PKI/CA mechanism. Finally, the advantages of the model are analyzed.