A comparative analysis of the floras of cyanoprokaryotes at European high latitudes was carried out. The analysis relied on information from the literature and data from own longterm research in the polar desert of the Svalbard archipelago. We sampled cyanobacteria in four sites of the North-East Land Island. Both original and published data on biodiversity were used in the analysis. The data were uploaded to the CYANOpro database (http://kpabg.ru/cyanopro/). The studied cyanoprokaryotes flora of European polar deserts has 176 taxa and is characterized by low diversity. The flora of the southerner tundra zone comprises 437 species. The similarity of the floras of European polar deserts and tundras is as low as 44 %. The causes of the low biodiversity are extreme ecological conditions – low temperatures, short growing season are limiting factors for the growth of most species. The studied floras of the North-East Land Island share much of their species composition. Differences between these floras are mainly due to the variation of geological conditions. Cyanoprokaryotes in Arctic ecosystems occupy a wide range of habitats. A notable reduction in the species diversity of typical aquatic cyanoprokaryotes from south to north is one of the main features of freshwater ecosystems at high latitudes. In polar desert conditions, the species composition and biomass of planktic and benthic cyanoprokaryotes are very poor. The cyanoprokaryotes diversity in the tundra zone increases markedly. There is a tendency for a reduction in the species diversity of the subaerophytic and aerophytic groups, but the areas occupied by cyanobacterial communities, on the contrary, increase, owing to a lower competition.