A total of 130 anvolatory infertile outpatients were divided randomly into 4 groups of LE1 (letrozole 2.5 mg,n =45),LE2 (letrozole 5 mg,n =30),CC1 (clomiphene citrate 50 mg,n =35) and CC2 (clomiphene citrate 100 mg,n =20).The treatments started at day 5 of menstruation and lasted for 5 days.The size and number of ovarian follicles and thickness of endometrium of all 4 groups were measured starting from day 10 of menstruation.8 000-10 000 units of human chorionic gonadotropin (hCG) was injected when ovary follicles were mature.And blood estradiol (E2) was measured at the same day.Ovulation,pregnancy and adverse reaction were also monitored.The pregnancy rate was 33％ (n =15) in group LE1 and 14％ (n =5) in group CC1 with significant statistical difference (x2 =4.00,P ＜ 0.05).And there were 43 successful ovulation periods in 55 periods with an ovulation rate of 78％ in group LE1;28 successful ovulation periods in 52 periods with an ovulation rate of 54％ in group CC with significant statistical difference (X2 =4.60,P ＜0.05).E2 level (pmol/L) in the day of hCG injection in group LE1 was (774.2 ± 126.0) pmol/L and in group CC1 (963.7 ± 108.3) pmol/L,t =3.98 with significant difference (P ＜ 0.01).The number of follicle in group LE1 was 1.20 ± 0.38;CC1 2.28 ± 0.88,t =4.76 with significant difference (P ＜0.01).The thickness of endometrium in the day of hCG in LE1 was (9.6 ± 1.3) mm;CC1 (5.9 ± 1.1) mm,t =6.20 with significant difference (P ＜ 0.01).No significant statistical differences existed between LE1 and LE2,CC1 and CC2 in pregnancy rate,successful ovulation,number of mature follicles,E2 level and thickness of endometrium at the day of hCG injection.The outcomes of 36 pregnancies were 32 full-term deliveries with neonatal health,2 early abortions and 2 prematures.Mild ovarian hyperstimulation syndrome (OHSS) had a low occurrence rate.