Species composition and taxonomic structure of phytoplankton communities in the main channel of the Amur at Khabarovsk (Russia) were monitored from spring to autumn of 2018–2019. In total, 187 species, varieties and forms of algae and cyanobacteria were found belonged to 8 phyla (Cyanobacteria, Bacillariophyta, Charophyta, Chlorophyta, Heterokontophyta, Rhodophyta, Euglenozoa, and Miozoa) and 75 genera. Diatoms formed the basis of the algal flora (94.7 % of the total species number). Mass vegetations of the diatoms and charophytes were observed with dominance of Asterionella formosa, Aulacoseira islandica, A. ambigua, A. granulata var. granulata, A. granulata var. angustissima, Ulnaria ulna, Diatoma tenue, Nitzschia acicularis, Stephanodiscus sp., Tabellaria flocculosa, Hannaea arcus var. rectus, Melosira varians, Fragilaria capucina var. vaucheriae, F. crotonensis, and Mougeotia sp. ster. Total number and biomass of plankton algae and cyanobacteria varied in the ranges of 1.74–5724.39 million cells/L and 2.5–2648.5 mg/L in spring-summer and 0.07–0.62 million cells/L and 0.2–1.4 mg/L in autumn. The water quality was evaluated by Pantle-Buck method modified by Sládeček as the betamezosaprobic III class (slightly polluted).