The rapid growth of knowledge in disease diagnosis and treatment requires health service provider organizations to continuously learn and update their practices. However, little is known about knowledge sharing in service implementation networks governed by a network administrative organization (NAO). The author suggests that strong ties enhance knowledge sharing and that there is a contingent effect of third-party ties. Two provider agencies’ common ties with the NAO may undermine knowledge sharing because of resource competition. In contrast, a dyad's common ties with a peer agency may boost knowledge sharing as a result of social cohesion. Finally, the author posits that third-party ties moderate the relationship between strong ties and knowledge sharing. These hypotheses are examined in a mental health network. Quantitative network analysis confirms the strong tie and third-party tie hypotheses and provides partial support for the moderating effect of third-party ties. The implications for public management, including the implementation of, are discussed.