Two new diatom species of the genus Aneumastus are described, A. laosica sp. nov. and A. genkalii sp. nov., based on light and scanning electron microscope observations. These species were found in Laos, and this is first finding of this genus from Southeast Asia. Almost all species from this genus were described and exist in Holarctic. Many species have restricted distributions and are known from fossil deposits, North America, Mongolia or local endemics of ancient lakes such as Baikal, Prespa and Ohrid. Diversity of Aneumastus species from these ancient lakes is higher than from waterbodies of the Holarctic region taken together. A few reports of this genus are from the southern Hemisphere (e.g. New Caledonia, Australia, Lake Tanganyika in Africa), but these taxon records are represented by a single valve only from every region and they require additional taxonomical investigation and verification to understand the full extent of the distribution of the genus.