The approach and structure of online networking have different implications for the knowledge sharing behavior of workers across teams within an organization. Despite studies on the topic, it is still not clear how the characteristic of social ties influences knowledge sharing behavior via online platforms, which have increasingly highlighted two opposing attributes: instrumental/task-related networks and expressive/personal networks. This study investigates the role of psychological defense in shaping the knowledge sharing behavior of employees in personal networking tools. Empirical analysis based on data collected from 455 knowledge workers demonstrated that psychological defense has a fundamental impact on knowledge sharing in personal networking context. Specifically, our results show that psychological safety, need to belong, self-integrity, sense of control, work overload, and role conflict have significant impact on the sharing behavior of knowledge workers in the personal networking context. The theory and practice contributions provided by the current study were discussed.