The aim of our study was to optimize the extraction of unfermented and fermented paste of cyanobacteria species A. platensis and to compare the content of total phenolic compounds (TPC) and antioxidant capacity (AOC) of aqueous and ethanolic extracts of unfermented paste extracts with fermented paste extracts. The paste underwent lactic acid fermentation with two different lactic acid bacteria (Lb. plantarum and Lb. brevis) for 24, 48 and 72 hours. The most effective was two-phase extraction (twice for 30 minutes) in water bath at 40 °C using distilled water or 96 % ethanol as extraction solvents. TPC was determined by the Folin-Ciocalteu method and the results were expressed as gallic acid equivalent. AOC was determined by DPPH· radical scavenging method and the results were expressed the as trolox equivalent. The highest TPC and AOC content were determined in aqueous extracts of unfermented paste (4.38 mM TPC and 1.40 mM AOC). The lowest TPC and AOC content was obtained in ethanolic extracts of unfermented paste (0.66 mM TPC and 0.46 mM AOC). In the case of aqueous extracts, the content of TPC and AOC was reduced by fermentation, while the content of TPC and AOC increased in the ethanolic extracts of fermented A. platensis paste. Subsequently, the extracts were dried and re-dissolved in a smaller amount of solvent (aqueous extracts with distilled water to obtain 50 mg dry matter/mL, ethanol extracts with dimethyl sulfoxide to obtain 100 mg dry matter/mL). With this procedure we have managed to preserve most of the antioxidants.