This study deals with the relationship between the project team's social network and knowledge accessibility from an empirical aspect. What kind of network structure is desirable to improve project team members' knowledge accessibility? Does a strong connection among group members improve their knowledge accessibility? Otherwise, does the expansion of the external network of a group improve its members' knowledge accessibility more efficiently? This study aims to contribute to developing existing network theories and knowledge management theories by answering these questions. To solve the raised research questions, a multi-level research model was developed on the basis of social network theory. From a social network analysis which was conducted on 172 consultants and 42 project teams in 5 global consulting companies doing business in Korea, it was found that the research results backed the existing two different social network mechanisms: closure mechanism and brokerage mechanism. However, the effect of social network on knowledge accessibility of project team members varied along the type of network involved. This study is meaningful in that it overcame the limits of the unit of analysis shown in existing studies by distinguishing group-level network density from individual-level network properties, and by analyzing the moderating effect between them.