The treatment of human erythrocyte membranes with superoxide anion (O₂^-_·) produced by pyrogallic acid, pH8.4, caused peroxidative damages to cell membranes, such as increase of fluorescent substance on membranes, formation of high molecular polymers (HMP) due to membrane protein cross-linking. However, these were almost not induced after adding a certain amount of Na₂SeO₃. It is suggested the anti-peroxidation effect of Na₂SeO₃ on erythrocyte membranes.