Аннотация:The freshwater diatom flora of southeast Asia is not well known. A few studies in the 19th century considered a small number of freshwater diatoms, and the 20th century also did not yield a large number of studies or endemic species (see Kulikovskiy et al. 2015). In the 21st century, the application of water quality monitoring led to more reports on the freshwater diatoms of the region. Our recent investigation of diatoms from this region has uncovered new species from the reservoirs of Vietnam using morphological and molecular approaches In this presentation, we will discuss species composition, rare and widespread taxa from Laos, Cambodia, Vietnam and comparison with Indonesia. Our study of different waterbodies from this region reveals many new species and we received additional data for a molecular phylogeny. The biogeography of diatoms from Southeast Asia will be discussed.