Objective To evaluate the efectiveness of different doses of letrozole on ovulation in infertility patients. Methods The databases such as CNKI,WanFang Data, PubMed and The Cochrane Librar were searched to collect randomized controlled trials(RCTs)and controlled clinical trials(CCTs)for the comparison of the effectiveness of different doses of letrozole in ovulation induction. The quality of the retrieved trials was critically appraised and Meta-analyses were conducted using RevMan 5.0 software. Results Eight studies were included and six of them were high quality. The results of Meta-analyses showed there were no significant differences between letrozole 2.5 mg and 5.0 mg in the diameter of mature follicle,ovulation rate,pregnancy rate and miscarriage rate,but there were significant differences in the endometrial thickness, follicular mature time and the number of mature follicles, letrozole 5.0 mg group led to thinner endometrial thickness,needed less time to achieve follicular maturity,produced more mature follicles. The indexes of effectiveness such as endometrial thickness,the number of mature follicles,ovulation rate,pregnancy rate, miscarriage rate were not statistically significant between lertozole 5.0 mg group and 7.5 mg group,there were significant differences in the follicular mature time, it needed less time to achieve follicular maturity in letrozole 7.5 mg group. Conclusions Letrozole at the dose of 5.0 mg per day led to thinner endometrial thickness,needed less time to achieve follicular maturity,produced more mature follicles and increased the rate of pregnancy. Letrozole at the dose of 5.0 mg per day can be recommended in clinical.