Reactive oxygen species are constantly formed in the human body and removed by antioxidant defenses. An antioxidant is a substance that, when present at low concentrations compared to that of an oxidizable substrate, significantly delays or prevents oxidation of that substrates. Glutathione plays an important role in the intracellular protection against oxidative stress and damage. The various estrogens and progestogens are known as antioxidants. We have evaluated the antioxidant effect of the HRT to postmenopausal women by measuring the amount of blood reduced glutathione(GSH). Also we have compared the amount of GSH of postmenopausal women with that of premenopausal women. We divided the postmenopausal women to three groups-women with estrogen only-Premarin 0.625mg daily(group 1), women with cyclic sequential regimen-Premarin 0.625mg daily and Provera 10mg for first 12 days of months(group 2), women with continuous combined regimen-Premarin 0.625mg and Provera 2.5mg daily(group 3). The blood GSH level was showed to increasing trends from pre-HRT to during-HRT, but this didnt show statistical significance. The blood GSH level of postmenopausal women was lower than that of premenopausal women significantly. We concluded that the antioxidant reserve of the postmenopausal women was increased during HRT and that postmenopausal women had less antioxidant reserve than premenopausal women.