A procedure is described for determining antioxidation activity of the water-soluble biological material. The procedure is based on the study of kinetics of the reduced 2.6-dichlorophenolindophenol oxidation by air oxygen both with and without the biological material as well as on calculation of the value for the constant of the biological material inhibition of 2.6-dichlorophenolindophenol oxidation as an index of the biological material antioxidation activity.