The reported prevalence of poor ovarian responders amongst patients undergoing IVF-ET is 9%-24%, and morbidity must be higher nowadays. For these women, Mild stimulation has been an important ovulation induction protocol. Clomiphene citrate(CC) and tamoxifen(TMX) are commonly used in mild stimulation protocol. It's reported that CC has adverse effect on growth of endrometrium and results in thin endrometrium(≤7mm) which maybe affect pregnancy rate. However, TMX has estrogen-like effect on the endrometrium that may be helpful to increase endormetrial thickness. The reported results about comparing CC with TMX showed that they had similar ovulation rate. Prospective study is necessary to confirm whether TMX is superior to CC on the IVF outcome.