Objective:To explore the ovulation induction efficacy of different doses of letrozole（LZ）and their effect on endometrium and sexual hormones in infertility patients. Methods:A total of 100 infertility patients were randomly divided into three groups. The patients of the first group（n=30）and the second group（n=32）were treated with LE 2.5 mg/d and 5 mg/d respectively for five days from 3 d of menses. The patients of the third group（n=30）took LE 20 mg on 3 d of menses. On the HCG injection day

follicle maturity days

number of mature follicles

endometrial thickness

serum estradiol（E2）

luteinizing hormone（LH）

testosterone（T）level

ovu lation rate

incidence of luteinized unruptured follicle syndrome（LUFS）and the level of E2 and progesterone on 7 d after ovulation were observed. Results:There was no significant difference in the 3 groups of HCG days after injection

follicle maturity days

number of mature follicles

endometrium thickness

E2

LH

T

ovulation rate and the level of progesterone in blood of 7 d after ovulation（all P >0.05）. There were significant difference in the 3 groups in the incidence of LUFS and the level of E2 in blood of 7 d after ovulation（P<0.05）. Conclusion:The therapy of all three groups can effectively promote the development of ovarian follicle

and ensure the endometrial thickness above 0.8 cm on HCG injection day

and the level of progesterone in blood higher than 60 nmol/L after ovulation.But only in LE 20 mg single oral group

blood E2 level can reach normal level of natural physiological cycle after 7 d of ovulation.Taking LE 20 mg on 3 d of menses is easy to perform

therefore is recommended as the first choice for LE ovulation induction program.