Abstract: OBJECTIVE To compare the efficacy of letrozole and human menopausal gonadotropin for treatment of clomiphene resisance polycystic ovary syndrome patients. METHODS 93 clomiphene resisance polycystic ovary syndrome patients conducted in the study were randomly divided into letrozole group(n=49) and HMG group(n=44). Patients in letrozole group received letrozole at 5 mg·d^-1 for 5 days on cycle days three to seven. Human menopausal gonadotropin 75 U·d^-1 was administered for 5 days starting from the third day of menstrual cycle in HMG group. Sonography was done for all patients, When mature follicle reached≥18 mm in diameter, HCG in a dose of 10 000 U was given. Transvaginal ultrasonography was performed for follicular diameter tracking and measurement of endometrial thickness. RESULTS The number of ovalution cycles was no significant difference in two group(78.91% vs 82.14%,P>0.05); The cycle number of ≥2 mature follicles was higher in HMG group than that in letrozole group(P<0.01). There were no significant differences comparing with cycle pregnancy rate(23.44% vs 24.11%, P>0.05) or miscarriage rate(6.67% vs 11.11%, P>0.05) in two groups. No multiple pregnancy was occurred in letrozole group, and 5 multiple pregnancy(18.52%, 5/27) in HMG group. On the day of HCG administration, endometrial thickness(9.88±1.96)mm vs (10.47±1.62)mm, P>0.05 was similar in two group. Serum levels of E2 and rates of ovarian cyst were significantly lower in letrozole group than those in HMG group. No ovarian hyperstimulation syndrome(OHSS) was occurred in letrozole group, rate of OHSS was 3.57% in HMG group. CONCLUSION There was no significant difference in either the ovulation rate or the pregnancy rate in clomiphene resisance polycystic ovary syndrome patients treated with letrozole or gonadotropin, but letrozole decreased the risk associated with treatment. Letrozole was an effective ovulation inducing agent.