Picoalgae (defined as cells smaller than 2-3 µm) include members of diverse taxonomic groups. They are an important constituent of marine plankton and ice biota and play a significant ecological role in biogeochemical cycles. Despite their importance, the true extent of their diversity has only recently been uncovered by molecular surveys. The diversity of picoeukaryotes has not yet been studied in the White Sea, which is a unique marine environment combining features of temperate and Arctic seas. Here, we investigated the taxonomic composition of eukaryotic picoalgae in ice and under-ice water at a station located in the Kandalaksha Bay of the White Sea. We applied metagenomic survey using Illumina sequencing. Eight main algae phyla, namely, Chlorophyta, Katablepharidophyta, Haptophyta, Dinophyta, Cercozoa, Bacillariophyta, Cryptophyta, and Ochrophyta were identified. The genera Paraphysomonas and Micromonas and the order Pedinellales were most numerous in plankton; the genera Paraphysomonas, Micromonas, and Metopion were most abundant in ice. The number of "rare" phylotypes was 80 in under-ice water and 112 in ice. Some taxa of nano- and microalgae are identified for the first time in the White Sea phytoplankton. Our data provide a basis for further research of tiny phototrophs in the Russian Arctic.