This paper discusses the relationship between psychological contract and knowledge sharing behavior in enterprise system post-implementation stage. The fulfillment and obligation of psychological contract are proposed as antecedents of knowledge sharing behavior performed by client firms. Additionally, the strategic concern is incorporated by addressing the moderating role of entrepreneurial orientation. Based on survey data collected from 132 client firms, psychological contract fulfillment is negatively related to knowledge sharing; whereas the positive role of psychological contract obligation is supported. The moderating effects of entrepreneurial orientation is significant as proposed by hypotheses. Discussion and implication are also provided.