The utilization of e-marketplace perceived to support users in seling their product. However, there are some difficulties faced by user in setting up the online space, utilizing the features and marketing their products. Hence, to minimize these bariers user could to share information and knowledge amongst them. Hence the objective of this study is to identify the motivations for knowledge sharing in online community. an online community format in Bukalapak.com an e-commerce website in indonesia were chose as the case study. social exchange theory, social cognitive theory and trust were studied as the basic theories in this research. we conducted quantitative approach with 105 respondents and analyzed the data using descriptive statistic. The result showed that self-efficacy, personal outcome expectation, community related outcome expectation from social cognitive theory are the motivations in knowledge sharing. in addition, of self-worth, enjoying helping, reciprocity and social support from social exchange theory are the motivations for sharing knowledge but not applied to reputation. information-based trust and identification were also identified as the motivations for sharing in online community.