Abstract: Objective： To evaluate the clinical efficacy of letrozole in treatment of clomiphene-resistant women with polycystic ovarian syndrome （PCOS）. Methods：Eighty-eight clomiphene-resistant women with PCOS were enrolled in this prospective，randomized，open-labeled study between Jan. 2010 and Jan. 2011. All subjects were divided into three groups andomly：the Letrozole group received Letrozole （LE） 2.5 mg/d per os for 5 days during days 3-7 of menstrual circle，the control group was administered HMG progressive increasing from 75 IU/d intramuscular. for ovulation induction on day 5 of menstrual circle；the LE+HMG group was treated with LE 2.5 mg/d for 5 days during days 3-7 of menstrual circle，from day 8，then treated with HMG 75 IU/d intramuscular. The transvaginal ultrasonography was applied to observe follicle growth and ovulation. When the follicular diameter was ≥18 mm in length，hCG （5000 IU） was injected to induce ovalution. Ovulation rate，pregnancy rate and the endometrial thickness were observed. Results：Ovulation rate and pregnacy rate were similar in three groups. The incidences of single dominant follicle in LE group and LE+HMG group were significantly higher than that in HMG group （P＜0.05），while the numbers of mature follicles in the LE group and LE+HMG group were lower than that in the HMG group. There was insignificant difference in endometrial thickness at the day of hCG injection among three groups. Conclusions：Letrozole can get good ovulation rate and pregnancy rate in those clomiphene-resistant women with PCOS. Compared with HMG alone，LE combined with HMG on the controlled ovarian stimulation can get higher ovulation rate with the lowered dose of HMG.

Key words: Polycystic ovary syndrome, Clomiphene, Menotropins, Clomiphene citrate-resistant