Environmental factors and water quality affect the distribution of freshwater snails. The purpose of this study was to investigate the effect of environmental factors the mollusks in constructed wetland. We set four sampling sites with different environmental condition such as BOD and plant cover in Chia Nan University wetland. Our results showed that the dominant species observed in the site with high BOD, and high diversity of freshwater snails related to high complexity in substratum. Our result this should can offer the design and maintain of constructed wetland in the future.