Abstract: Market access plays an important role in increasing smallholder’s income; however, informal markets are typical in developing countries. Traders often dominate agricultural markets. In Vietnam aquaculture, collectors are important actors and act as an intermediary in linking farmers and buyers. This research aimed to explore and analysis the functions and the dominance of collectors in linking with smallholder fish farmers in Tam Giang lagoon, central Vietnam. The qualitative research is applied through 55 semi-structured interviews including smallholder fish farmers, collectors, wholesalers, retailers, officers of local government and second information from statistic data and reports. The research findings showed that linking of smallholder fish farmers to output market has dependence on collectors while all aquatic products have to pass on collectors before distributing to next buyers. Collectors always have strategies to maintain the relationship with smallholders and they always have an advantage status in aquaculture value chain. Collectors are also considered as a barrier of smallholder farmers to access potential marketing channels. Informal transaction and trust are characterized in the interaction between collectors and smallholders.