The open access fisheries regime has led to the degradation of marine resources and to
conflicts in sharing them and the fishing grounds in Tam Giang Cau Hai lagoon in Thua
Thien Hue, Vietnam. In 2003, community-based fisheries management (CBFM), particularly through Fisheries Associations (FA), was introduced and established. As of 2011, there were 62 local FAs. It means that local FAs have played an important role in the implementation of CBFM and as a major partner of the Government in protection of aquatic resource and fisheries management. This study highlights the demands of implementation, level of awareness and participation, effectiveness and weakness and methods for measuring the transaction costs in Giang Xuan FA in particular and fisheries Co-management system in general. The study also demonstrates the transaction cost concept and approach for assessing such costs in fisheries Co-management systems.