Polycystic ovary syndrome (PCOS) is a common disease that has an effect on approximately 10% of women of childbearing age. Although there is evidence regarding the role of lifestyle factors in the development of PCOS, the exact etiology remains unclear. Additionally, metformin is used in the treatment of PCOS but its role remains unclear. We compared the effects of lifestyle modification (LSM) + metformin and metformin alone on PCOS. We performed a systematic review by searching electronic databases for publications until December 2019. The primary endpoints were clinical outcomes, such as menstrual cycles and pregnancy rates, and the secondary endpoints were anthropometric, metabolic, and androgenic parameters. The meta-analysis revealed that there was no significant difference in the improvements in the menstrual cycles between LSM and metformin alone (weighted mean difference [MD] = 1.62) and between LSM + metformin and LSM (MD = 1.20). The pregnancy rates and body mass indices were not significantly different between LSM and metformin alone (MD = 1.44 and -0.11, respectively). LSM reduced insulin resistance (MD = -0.52) and increased serum levels of sex hormone-binding globulins (MD = 8.27) compared with metformin. Therefore, we suggest recommending lifestyle modifications actively to women with PCOS if they do not have indications for metformin.