This paper integrates expectancy disconfirmation theory and justice theory to construct a model for investigating the motivations behind people’s knowledge sharing in open professional virtual communities. The study holds that three dimensions of positive disconfirmation (i.e., knowledge quality, self-worth, and social interaction), three dimensions of justice (i.e., distributive, procedural justice, and interactional), and playfulness will influence individuals’ satisfaction with knowledge sharing in open professional virtual communities. We also argue that playfulness and satisfaction can engender knowledge sharing continuance intention in such communities. Data collected from 270 members of one open professional virtual community provide support for the proposed model. The results help identifying the motivation underlying individuals’ knowledge sharing behavior. Implications for theory and practice and limitations are discussed.