Abstract In April 2018, complex studies of phytoplankton communities were carried out in the northwestern Barents Sea in the region of the Polar Front (74.8°-76.2° N) in a layer of 0-50 m. The region under study encompassed surface Arctic water and Atlantic water of the Fram branch (which conditionally corresponds to the Arctic water mass) divided from the Atlantic water mass by the Polar Front. Phytoplankton community on both sides of the front were represented by early spring complex, 90% of biomass was formed by diatoms (Achnanthes taeniata, Nitzschia grunowii, Thalassiosira antarctica). In water of Atlantic origin Phaeocystis pouchetii were found among the dominants. However, the level of development of microplankton was significantly higher in water from the Arctic Basin. The highest chlorophyll-a concentrations referred to surface Arctic water (3.13±0.43 mg/m3) and Atlantic Fram water (2.04±0.29 mg/m3). The concentration of chlorophyll-a at the stations performed in the Atlantic water mass was an order of magnitude lower - 0.50±0.26 mg/m3. Thus, during the early-spring period, the Polar Front is a powerful boundary that limits exclusively the level of development and quantitative indicators of the early spring microphytoplankton complex. The front line separates the more productive Arctic water, with average chlorophyll-a concentrations of 2-3 mg/m3, from the Atlantic water, in which concentrations of this pigment are an order of magnitude lower.