In order to investigate the structure of phytoplankton communities, this study was carried out at 37 stations from July 19 to September 5, 2008 in the Bering Sea, Chukchi Sea and Canadian Basin. Phytoplankton communities were composed of 71 taxa representing Dinophyceae, Cryptophyceae, Bacillariophyceae, Chrysophyceae, Dictyochophyceae, rasinophyceae, Prymneosiophyceae and unidentified phytoplankton(< 20㎛) in the study area. Phytoplankton standing crops ranged from minimum 2.19×105cells ℓ-1 at station D84 to maximum 8.29×106cells ℓ-1 at station R09 in the study area. The most abundant species was nano-pico sized phytoplankton in almost station, but the second was variable. Phytoplankton dominant species were Thalassiosira sp., Chaetoceros sp. and nano-picophytoplankton such as Dinobryon belgica and Cryptomonas sp.. There were positive correlations between phytoplankton biomass and physical factors. From western Bering sea to Bering strait the biomass was more higher, but after through the Bering Strait it was more lower along latitude to the arctic. 1) To investigate on species composition, abundance and dominant species of phytoplankton communities in the Bering Sea, Chukchi Sea and Canadian Basin 2) To study on taxonomic research and dominant species of phytoplankton communities for investigate on indicator species