Here we describe two new Hydrovatus species (Coleoptera: Dytiscidae: Hydroporinae: Hydrovatini) from the province of Khon Kaen, Isan region in NE Thailand. Hydrovatus is the third most species rich genus of diving beetles (Dytiscidae). It occurs on all continents except Antarctica and now numbers 210 currently recognized species. Both new species, Hydrovatus diversipunctatussp. n. and Hydrovatus globosussp. n., were collected at lights and are only known from the type locality "Khon Kaen" (a city and province). Diagnoses based on morphology for the separation from closely related species are given together with illustrations of male genitalia and habitus photos. We provide a determination key to Old World species of the pustulatus species group and to Oriental species of the oblongipennis species group.
Keywords: Coleoptera; Dytiscidae; Hydrovatus; Thailand; keys to species; new species; taxonomy.