Objective: To evaluate of metformin effectiveness of ovulation induction treatment in polycystic ovary syndrome (PCOS) women. Methods: Eight databases and nine related journals were searched for randomized controlled trails (RCTs) on the comparison between metformin and clomiphene citrate used for PCOS women. Meta analysis was performed after quality assessment. Results: Ovulation rate in metformin group compared with clomiphene citrate group was lower with a significant difference [OR = 0.48 (0.26-0.87), p = 0.01]; no significant difference was found for pregnancy rate [OR = 0.94 (0.26-3.43)], miscarriage rate [OR = 0.63 (0.06-6.47)] between two groups. Compared with the combination of metformin and clomiphene citrate group, pregnancy rate in metformin group was significantly lower [Peto OR = 1.56 (1.16-2.08), p = 0.003], but there was no significant difference in the two groups about ovulation rate [OR = 1.52 (0.95-2.45)], miscarriage rate [Peto OR = 1.40 (0.79-2.48)]. Conclusions: Compared with clomiphene citrate, metformin used for ovulation induction treatment in PCOS women, can promote ovulation induction and pregnancy rate, the effect of the combination treatment is better than that of a single drug use.