This research was conducted to generate a primary database on ichthyofauna,distribution and diversities in the upstream and downstream segments of Sittaung River in Bago Region of Myanmar.This study contributes to the information needed on the distribution of river fish in Myanmar.Fish diversities are assessed by calculating the various diversities indices between December,2018 and November,2019.A total of 65 fish species belonging to 9 orders,23 families and 49 genera were recorded.All 65 fish species were found in upstream segment but only 60 species of them were found in downstream segment of the river.In all study sites,Shannon diversity index had value above 3 indicating that the structure of habitat was stable and balanced.Simpson’s index values were close to 1 in all sites indicating that the species richness in the region was satisfactory.The abundance all of above 5%of total catch of Mystus vittatus,M.pulcher,M.cavasius and Erethistes pusillus in their feeding habitat suggested that their upstream and downstream habitats provided suitable feeding conditions.Anguilla bengalensis,Tenualosa ilisha,Mystus gulio,Rita rita and Silonia silondia were least abundant all below 0.1%of total catch showing they could be impacted by unwise anthropogenic activities.Assessing fish species diversity is thus very important to conserve and manage and promote the health of river ecosystem that is necessary for the migration of fish species.