Knowledge sharing among project team members has been recognized as a critical determinant for the success of a project. Thus, understanding the factors that increase knowledge sharing is important academically and practically. This study focuses on the relationship between a team member’s cultural values and their intention to share knowledge within a project team through social capital (SoC). SoC is formed in a social network of team members and may influence knowledge sharing within a group. We also investigate the role of web-based communication (WBC) media richness as a moderator for the relationship between cultural values and social capital. The results show that social capital is an important factor in knowledge sharing. Espoused collectivism and low power distance provide a positive influence to social capital formation. Furthermore, the WBC media richness positively moderates the relationship between collectivistic values and social capital. The results of the study can provide project managers with insightful suggestions on how to encourage project team members to share their knowledge.