Electronic word-of-mouth (eWOM) plays a major role for customer decision. Through blogs and forums, company may use eWOM to maintain a better customer relationship through customer knowledge sharing. This study adopts a cost-benefit framework to predict the users' contribution behavior. In this model, we provide four benefits (reputation, reciprocity, enjoy helping, self-efficacy) and two costs (convenience and interaction). E-tailers may be able to use the results of this study to enhance customers' knowledge sharing intention in their blogs or forums.