Experimental pharmacological research of 1-[2-(R-phenylimino)-4-methyl-3-(3-[morpholine-4-yl]propyl)-2,3-dihydro-1,3-thiazol-5-yl]ethane-1-one derivatives. Determination of the nature of the effect of electron-donating and electron-withdrawing substituents in the phenyl fragment of the molecule on expression of the antioxidant activity. Analysis of some aspects of the "structure–activity" relationship. Derivatives of 1-[2-(R-phenylimino)-4-methyl-3-(3-[morpholine-4-yl]propyl)-2,3-dihydro-1,3-thiazol-5-yl]ethane-1-one were synthesized by Hantzsch method. Experimental pharmacological research was carried out on the model of artificial oxidative stress using the emulsion of egg-yolk lipoproteins in vitro as a substrate of oxidation. The substances of group 1 with methyl substituents and group 2 with chlorine substituent posseses pronounced antioxidant activity. The substances of group 2 with methoxy substituent posseses moderate antioxidant activity. Introduction of any substituents leads to a significant change in the level and direction of antioxidant activity of the substances; and it depends on the chemical nature and orientation of the substituents in the phenyl fragment of the molecule. Among the compounds under research four compounds can be recommended as potential antioxidants for further screening studies.