Based on specimens (Natural History Museum Vienna, Cambodian Entomology Initiatives at the Royal University of Phnom Penh, private collection of fourth author) and based on literature, we provide a first species list of aquatic Hemiptera (Gerromorpha and Nepomorpha) of Cambodia. We studied 38 species (37 identified) and added three reliable species records from the literature. In total, we report on 41 species in 25 genera and 11 families (Belostomatidae, Gerridae, Hebridae, Helotrephidae, Hydrometridae, Mesoveliidae, Micronectidae, Naucoridae, Nepidae, Notonectidae, Veliidae). Most of these taxa are recorded from Cambodia for the first time. We describe two species as new to science: Microvelia falcata sp. n. (Veliidae) and Ranatra cardamomensis sp. n. (Nepidae). Subspecific rank is given for Cylindrostethus costalis malayensis Polhemus, 1994 stat. n. (Gerridae) that was formerly described as a distinct species.