The topography of Thailand is characterized by low-lying agriculture lands abruptly punctuated by discontinuous mountain ranges, with their associated streams and aquatic insect communities. Water striders (Gerridae) are common members of these communities are. Seventy-nine species representing 22 genera were collected from Thailand, including 21 undescribed species and four new country records. The similarity of Gerridae communities was examined among isolated mountain ranges and between lowlands north and south of the Isthmus of Kra. Concordance in biogeographic patterns among mountain ranges was evaluated using two-way indicator species analysis and cluster analysis.