The taxonomic composition of benthic diatoms in Grønfjord Bay (Western Spitsbergen) was studied during the polar night. Living cells of 47 diatom species were identified in the benthic communities, with pennate forms overwhelmingly predominating, which is typical of the microphytobenthos of the Arctic coast. At the studied stations, the total number of diatom species varied within relatively narrow limits – from 31 to 40 taxa. The maximum species richness (40 species) was recorded at station 2. The core of the benthic microalgae communities in Grønfjord Bay were typically benthic forms, represented by 35 taxa. The quantities of planktonic and planktonic/ice diatoms were minor – 3 and 2 species, respectively. Marine (27 species) and brackish-marine (15 species) forms predominated in the microphytobenthos. Freshwater forms were present only sporadically and as singular specimens. The Jaccard floristic similarity coefficient for pairs of stations ranged from 55.5 to 60 %, i.e. within moderate to high similarity range. The results indicate that a viable diatom community maintaining metabolic activity exists in the benthos even during the polar night.