Antipyrinethiosemicarbazone derivatives have been investigated as antioxidant in this work. The results of antioxidant activity coefficient (K) proved that all investigated compounds have good antioxidant activity. Investigation of the relation between antioxidant activity (K) and quantum-chemical parameters difference of heats of formation of a molecule and its cation radical ΔHf shows that the ΔHf values proportional with K values of investigated compounds.