The antioxidant activity of two new series of pirolidinium chlorides (PAC-n) and bromides (PAB-n) was studied. The antioxidant functional group was incorporated into the polar part of the compounds. The influence of the compounds on the degree of lipid oxidation in the erythrocyte membrane subjected to UV radiation was studied. It was found that all the salts used protected erythrocyte membranes against oxidation of membrane lipids. Their antioxidant activity increased with alkyl chain length. PAB compounds were stronger oxidation inhibitors than PAC ones. Possible reasons for such behaviour are discussed, taking into account the fluidity changes in erythrocyte membrane caused by the compounds studied. In order to do this, steady-state measurements of fluorescence anisotropy were performed, enabling to calculate the anisotropy coefficient.