An assessment on the fishery and socioeconomic status of fishing communities at the Thanlwin River Estuary, Mon State has been conducted within the period of 2015-2018 especially at Kalwe and Ahlat Village tract, at Belukyun Island which is situated at the mouth of the Thanlwin River. The regions are well-known for brackish and marine water fisheries even the mudflat fisheries as well. The common fishing gears employed in this area are beach seine net, bag net, and the drift gill net. A total of 24 species of brackish and marine fishes were recorded from the estuary. Group interviews were conducted with local peoples, along with surveys into the fishing areas. Among the recorded fish species, the brackish fish species of Polynemus paradiseus (Paradise threadfin), Tenualosa ilisha (Helsa) and Johnius coitor (Coitor croaker) are the important commercial fishes found around the estuary. The estuarine environment is experiencing the rhythm of dynamic hydro-sedimentation such as alternate erosion and accumulations mostly at the river mouth epically near the Belukyun Island. Local fishery communities are trying to adapt to the environmental and consequent changes of socio economy and livelihoods. Unfortunately, local communities are nowadays facing the problems of yearly depletion of fish catches around these areas. According to local information, some fish species are on the verge of complete disappearance, some commercial species have become rare and some are now totally vanished from the area. Accordingly the socio-economy status of the region also is changing among the local communities. So that, enhancing the aquaculture system within the country is become important issue and need to introduce the technology within the possible regions.