Forumns or discussion boards are one of the most vital internet applications used for communication and knowledge sharing. forumns are known as a kind of knowledge sharing mechanisms, where people can get involved in the topics of their interests. in general of e-commerce, and e-marketplace in particular, forums are used to assist members in interaction and communication of their experiences regarding business transactions, as well as to create trusting environment among members in e-marketplace. base on social cognitive theory (SCT), this study investigated the relationship between trust among individuals who used discussion forums and their behavioral intentions reflecting a possibility to follow advices and/or make a purchase of products in the future. a total of 240 respondents were collected from five leading e-marketplaces in thailand. the results show positive relationships between trust variables and behavioral intention. self-efficacy in using forums is also vital in creating affective temper, which leads to trust formation.