Aim In order to study effects of estrogen on endothelium dependent vasodilatory function. Methods 32 healthy postmenopausal women regarded as estrogen replacement therapy (ERT) group were treated with conjugated equine estrogen 0.625 mg per day for two weeks, and 24 healthy premenopausal women were regarded as control group. Flow mediated vasodilatory response(FMD) of the brachial artery in ERT and control group were measured by use of high resolution ultrasonography method. Plasma lipids, nitric oxide(NO) and estradiol(E₂) level were also measured. Results Compared with premenopause, plasma E₂ and NO level were significantly decreased(p<0.001), and FMD of the brachial artery also were significantly reduced in postmenopausal women (FMD: 10.05%±3.18% vs. 3.84%±2.18%, p<0.001). After short term ERT, plasma E₂ and NO level were significantly increased(p<0.001), and FMD of the brachial artery also were significantly improved in postmenopausal women (FMD: 9.16%±3.02%, p<0.001), while plasma lipids had no significantly changes before and after ERT. Multiple linear stepwise regression analysis showed that FMD of brachial artery was positively related to NO and E₂(r: 0.729, 0.564, respectively, p<0.001), and was negative related to TC level (r:-0.369, p<0.05). Conclusions Short term ERT can reverse endothelium dependent vasodilatory dysfunction in postmenopausal women. This improvement is not dependent on plasma lipids level, but may be related to the direct vascular protective effects of estrogen, which may be involved in the anti atherogenic action of estrogen.