Backgraund: Oxidized-low density lipoprotein (ox-LDL) plays an important role in the pathogenesis of atherosclerosis. Hormone replacement therapy (HRT) reduces the increased risk in coronary heart disease (CHD) in postmenopausal women. It is proposed that estrogen and progesteron have antioxidant effects in addition to other cardioprotective effects. From this point of view, we planned to examine the susceptibility of apolipoprotein B containing lipoproteins (non-HDL fraction) to oxidation in HRT-receiving (HRT-group, n:33) and nonreceiving menopausal women (M-group, n:33). Methods: In this purpose we incubated the non-HDL fraction with copper sulphate after separating it by precipitation method. Then, we measured malondialdehyde (MDA) levels every half hour for 3 hours and determined the lag time which is the interpretation of susceptibility of lipoproteins to oxidation interms of time. Results: In our study lag time was unexpectedly shorter in the HRT-group than that in the M-group (p < 0.05). There was no significant difference between the serum MDA levels between the groups. Vitamin E, uric acid and ferritin were significantly (respectively, p < 0.01, 0.01, 0.001) higher in serum of M-group than those in the HRT-group, while transferrin level was found to be significantly higher (p < 0.05) in the HRT-group. Conclusion: As a result, we have got the opinion that: in addition to HRT, antioxidants may have effects in protecting non-HDL fraction from oxidation and women from CHD.