The research focuses on "Illegal Fishing Management in Lower Sesan 2 Reservoir, Stung Treng Province, Cambodia" with two research objectives: to understand the illegal fishing situation and to explore solutions to address the illegal fishing issues in the Lower Sesan 2 Reservoir. The research is approached by a Conceptual Framework addressing four elements of illegal fishing in the Lower Sesan 2 reservoir.The livelihoods of local fishers and migrant fishers in Lower Sesan 2 reservoir were identified: fishing, rice production, farming, animal husbandry NTFP collection. Some local fishers and all migrant fishers including men, women and youths carried out illegal fishing in Lower Sesan 2. They used illegal fishing gears, caught endangered fish species, fished in conservation area, fished with illegal fishing gears in close fishing season, trading fish without license. The causes of illegal fishing in Lower Sesan 2 reservoir were found out. The performances and challenges, opportunities of stakeholders in fishery resource management in Lower Sesan 2 were identified. The strategies of sustainable fishery resource management were found out. Some recommendations were produced.