The invention relates to chemistry and medicine, namely to a biologically active coordinative nickel compound from the class of transition metal thiosemicarbazonates. The compound exhibits high antioxidant activity and can find application in medicine as a substance that inhibits the oxidation processes of organic molecules in the human body.Summary of the invention consists in producing a synthetic antioxidant based on [4-(2, 4-dimethylphenyl)-2-(2-hydroxy-3-methoxybenzylidene)hydrazinecarbothioamide-S][4-(2, 4-dimethylphenyl)-2-(oxo-3-methoxybenzylidene)hydrazinecarbothioamido(2-)-O, N, S]-nickel(II) monoethanol solvate of the formula : The claimed compound expands the arsenal of synthetic antioxidants with high biological activity.