The water strider subfamily Ptilomerinae (Heteroptera: Gerridae) includes common inhabitants of fast-flowing montane streams in Thailand. Eleven species representing five genera previously were recorded from Thailand. Recently, three undescribed species of Ptilomera were collected from the western and southern regions of the country. In addition, a new species of Rhyacobates was collected from northern Thailand. This brings the number of species of this subfamily in Thailand to 15. Two-way Indicator Species Analysis was used to examine concordance in biogeographic patterns among species of this subfamily. Further, analysis of variance was used to determine if species richness of this subfamily differs among mountain ranges. Ecological and biological information also are presented herein.