Picoplankton are particularly small phytoplankton with sizes between 0.2 and 2 mu m and mostly include chroococcoid cyanobacteria, Synechococcus spp. They are major contributors to the total autotrophic biomass in the oceans. The importance of this group has increased in recent years. The aim of the study is to determine the geographic variation of picoplanktonic Synechoccocus spp. biomass along the Anatolian coast during late autumn. The sampling program was carried out from October 15 and 11 November 2013. Sample were collected from surface water of 57 station which were located between the coast line and 15 miles off between Igneada-Hopa. Physico-chemical properties of sea water like temperature (degrees C), salinity (ppt), sigma-t, conductivity (S m(-1)) and Dissolved Oxygen (mg L-1) were also collected from each station with Sea & Sun Tech M75 CTD profiler. Autotrophic picoplanktonic cells were counted by using ACCURY C6 flowcytometer. Results were given as cells ml(-1). Sea surface temperature ranged between 16.2-18.2 degrees C. Stagnated water was observed from surface to 20 m and thermocline developed between 35-60 m. Our results showed that picoplankton concentrations increased in recent years in the coastal area of Southern Black Sea. The lowest and the highest Synechococcus spp. concentrations were found as 7.4x10(3) cells ml(-1) and 9.2 x10(4) ml(-1) in Sile off and mouth of Kizilirmak River respectively. The results indicate that Sile and Kizilirmak area shown different picoplanktonic structure among the other sampling region.