Objective To assess the effectiveness of letrozole in ovulation induction treatment. Methods We searched CBMdisc (1979 to 2009), Wanfang (1994 to 2009), CNKI (1994 to 2009), VIP(1989 to 2009), PubMed (1997 to 2009), PML (1997 to 2009), FMJS(2000 to 2009) and 9 relevant journals to identify randomized controlled trails (RCTs) comparing letrozole with clomiphene citrate in ovulation induction treatment. The quality of the included trials was critically appraised. RevMan 4.2.7 software was used for statistical analyses. Results Ten RCTs involving 3100 patients were included, among which 5 RCTs were graded A, 4 were graded B, and 1 was graded C. Five RCTs showed that endometrial thickness at the time of human chorionic gonadotrophin (HCG) administration in the letrozole group was significantly higher than that in the clomiphene group. One RCT showed that endometrial thickness at the time of HCG administration in the letrozole group was significantly lower than that in the clomiphene group. Three RCTs showed no significant differences between the two groups. Four RCTs showed that the number of dominant follicle at the time of HCG administration in the letrozole group was signficantly lower than that in the clomiphene group. One RCT showed that the number of dominant follicle at the time of HCG administration in the letrozole group was significantly higher than that in the clomiphene group. Two RCTs showed no significant differences between the two groups. Compared with clomiphene citrate, the pregnancy rate in the letrozole monotherapy group was slightly lower at the RR 1.03 and 95%CI 0.82 to 1.29, pregnancy rate in the combination group was higher at RR 1.73 and 95%CI 1.37 to 2.18. The ovulation rate in the letrozole group was higher and no significant differences were found between the two groups at RR 1.23 and 95%CI 0.97 to 1.57. Conclusions There may be differences between letrozole and clomiphene citrate in ovulation induction treatment in terms of endometrial thickness, number of dominant follicle, ovulation rate, and pregnancy rate, but no significant differences. Letrozole can make up for the shortcomings of clinical clomiphene in ovulation induction and serve as an alternative. This conclusion needs to be further confirmed through more well-designed, multi-centered, large-sample RCTs.