High intensity salt stress mainly decreases the content of phycocyanin in cyanobacteria, including spirulina, and thereby interrupts the energy transfer from phycobiliproteins to PS2 reaction center. Salt stress increases the accumulation of NaCl in the cytoplasm of cyanobacterial cells, affects growth rate, and is often associated with decrease in photosynthetic electron transport activities in photosynthesis. As a result, the high concentration of NaCl results in irreversible metabolic changes in the susceptible strains. The antioxidant capacity of Arthrospira platensis (Spirulina) cultivated for 6 day at a temperature of 32-35ºС with different quantities of NaCl added to the medium (0.043M; 0.085 M; 0.342 M; 0.684 M and 0.017 M as control) was measured using Photochem instrument from AnalytikJena. The highest antioxidant value was obtained for NaCl concentration of 0,043 M, 63,55 μg TROLOX/ml product. The lowest antioxidant value was obtained for NaCl concentration of 0,684 M, 9,61 μg TROLOX/ml product. A drastic decrease in antioxidant activity in biomass was observed.