The knowledge sharing process within a virtual community of teacher professionals is viewed as a social exchange process in that the knowledge sharing intention and behavior of individuals are influenced by the exchange relationship among members. However, relatively little research has focused on this approach to exploring the factors that enhance the knowledge sharing of individuals. This study aims to explore the mechanism of how individuals' knowledge sharing intention and behaviors might be altered with a sample of 332 teachers within a virtual community of teacher professionals (i.e., SCTNet) in Taiwan. After controlling for the technology support factors (i.e., perceived usefulness and perceived ease of use), we found that community trust impacts knowledge sharing intention, which in turn improves knowledge sharing behavior. Furthermore, altruism augmented the relationship between community trust and knowledge sharing intention. The positive relationship between community trust and knowledge sharing intention was stronger when teachers perceived a high level of altruism than it was with a low level of altruism.