The naturally occurring radionuclide 210Po was determined in different components of the Black Sea ecosystem. The specific activity of 210Po in water in the open part of the sea was about 1Bq ⋅ m-3. The range of 210Po specific activity in bottom sediments was 4.5–500 Bq ⋅ kg-1 dry weight depending on their type, area and depth of collection. The highest values were found in the NW part of the Black Sea. Sediment distribution coefficients (Kd) of 210Po for bottom sediments, calculated on a dry weight basis, varied from 0.5 × 104 to 5 × 105. The levels of 210Po specific activity in molluscs and pelagic fishes anchovy and sprat were the highest among the investigated species of the Black Sea biota. Concentration factors (CF) of 210Po, estimated on a wet weight basis, reached 1.5 × 103 for macrophytes, 4 × 103 for total zooplankton, 103–104 for the entire fishes depending on their ecological groups affiliation and (0.7–6.0) × 104 for molluscs. So, the ability of the Black Sea biota to accumulate the natural radionuclide 210Po is comparable with that of similar species from others marine and oceanic areas.