The study was carried out on Cu Lao Dung (CLD), a small island located in the lower Mekong River, in SocTrang province. The objective of the study was to survey the diversity of species composition and biodiversityindexes of vascular plants here. Since then, the environmental quality has been initially assessed throughthe research plant group. The study was carried out in 2 years (2018-2020) with qualitative research (followingthe sampling route) and quantitative research (collecting samples in standard plots. The results of speciescomposition diversity obtained 106 species belonging to 88 genera, 49 families of 2 phyla. The ten mostdiverse plant families here account for 53.77%. The canal habitat was the habitat with the most species.Woody plants were the dominant group in terms of life forms. The plants in the study area were usedmedicinally with the rate of 91.51%. Biodiversity index results showed that Sonneratiacaseolaris was auniformly distributed species and was also the dominant species in CLD mangroves. Mangrove forests inCLD were tropical plantations and were stable. Nypafruticans was the predominant species in lagoon habitatsand inundated areas inside and outside the dyke. The groups of plants in this habitat have been greatlyaffected by relatively stable environmental conditions. The habitats of rivers, canals and lowland gardenswere the habitats with the most species. The biodiversity index H reached 5.48, which was an adaptiveenvironment for aquatic plants in the study area.