A study on fish diversity was conducted from August 2019 to June 2020 in Cu Lao Dung, which is located in the estuarine areas of the Mekong River. Fish and water samples were collected from 4 habitat types (represented by the 12 considered sampling sites: river/canal, garden pond, aquaculture farm and mangrove) by using hand nets, seine nets and measuring equipment. 67 species belonging to 22 families and 9 orders were identified. The most abundant order, containing 43 species (64.18%), was the Perciformes, and the least abundant were the Synbranchiformes and Tetraodontiformes, containing only 1 species (1.49%). The results also indicated that salinity had affected the distribution of the fish composition. The number of fish species in the mangrove habitat was higher than in other habitats. The highest number of species collected in the mangrove habitat was 54 species (80.60%), followed by the garden pond habitat, with 38 species (56.72%), the river/canal habitat, with 36 species (53.73%), and the aquaculture farm habitat, with 35 species (52.24%). The results showed 56 species (83.58%) in the rainy season and 53 species (79.1%) in the dry season, with the Perciformes as the most abundant order, with 35 species (66.04%) in the dry season and 34 species (60.71%) in the rainy season.