Description: The Antarctic cyanobacterial microflora is one of the main components of the diversity of freshwater phototrophic communities in coastal areas. It is little known according to the modern taxonomic criteria (polyphasic approach). Populations of heterocytous cyanobacteria from Ulu Peninsula, the northern part of James Ross Island, NW Weddell Sea, Antarctica, were therefore reviewed. The identified morphospecies were compared with specimens from other localities in maritime Antarctica, especially from the South Shetland Islands. Ecological demands, morphological variations and, if possible, their phylogenetic positions (based on 16S rRNA gene sequencing) of registered populations were analyzed. Altogether, 11 species of heterocytous cyanoprokaryotes were recognized and studied in detail. These species were dominant in the characteristic habitats, and four novel species were described. All have a restricted endemic Antarctic distribution according to both morphology and 16S rRNA gene analyses. Three species of the genus Calothrix, one species of the genus Dichothrix (Rivulariaceae), and four species from the family Tolypotrichaceae were recognized and documented. Few species from this family belong to the recently recognized and revised genera Dactylothamnos and Hassallia, based on molecular analyses. Nodularia quadrata and two species, taxonomically classified to the genus Hydrocoryne (Nostocaceae), were studied. The complex of the genus Nostoc (especially of N. commune ) exists as numerous morpho- and ecotypes, and it is diverse phylogenetically, morphologically and ecologically, and will be analyzed in special studies. Our study is important for the exact identification of cyanobacterial microflora in Antarctica, which plays a dominant role in the colonization of deglaciated areas.