Abundance and biomass of picoplankton which are major component of the marine microbial food web with physicochemical environmental variables were monitored monthly in the south-eastern Black Sea during late spring 2010. According to our results Synechococcus spp. abundance range from 3.67 x 10(5) - 6.58 x 10(8) cells L-1 whereas biomass range from 0.15-23.9 mu g C L-1. Maximum abundance and biomass of Synechococcus spp. were found at 1% light level at June 2010. The minimum and the maximum heterotrophic bacterial abundance and biomass ranged between 1.14x10(9) - 3.63x10(9) cells L-1 and 6.24-76 mu g C L-1, respectively. Heterotrophic bacteria made a higher contribution to picoplankton biomass on the region, while picophytoplankton became more important within the microbial food web at 30 m in June. The ratio of bacterial carbon (integrated 30 m) to phytoplankton carbon was 0.69, 0.24, 0.49 at April, May and June, respectively. In the top of 20 m water column phytoplankton carbon biomass was 2-3 times higher than picoplankton. Below this depth, however, picoplankton represented the dominant fraction in terms of carbon biomass (50-75%).