Objective To assess the efficacy and safety of thiazolidinediones combined with metformin in treatment of polycystic ovary syndrome.Methods Electronic database searching was performed on Medline, Cochrane Library, EMbase，EBSCO，ScienceDirect，OVID，Springer LINK，Wiley，Chinese biology and medicine(CBM), China National Knowledge Infrastructure (CNKI), and Chongqing VIP Database; meanwhile, unpubished literature, conference papers and dissertations were also searched manually. The data included those from the establishment to November 2009. Randomized or clinical controlled trials concerning the thiazolidinediones and metformin combination therapy for PCOS were selected and assessed for the methodological quality, and Meta-analysis was performed using statistical software Revman 5.0.Results Five randomized controlled trials met the inclusion criteria and were included. Compared to metformin group, thiazolidinediones combined with metformin significantly improved insulin resistance(P<0.000 01,WMD=-0.21,95%CI［-0.27，-0.15］) and ovulation rates(P=0.003, OR=2.76,95%CI［1.14,5.42］) . There was no difference in WHR(P=0.51,WMD=0.02,95%CI［-0.04,0.08］) and serum testosterone(P=0.20,WMD=-31.14,95%CI［-79.21，16.92］) between the combination and metformin groups. However, single metformin therapy was shown to have more benefit in ameliorating BMI(P=0.02,WMD=0.54,95%CI［0.08，1.00］) than the combination group. There were no serious adverse events during the treatment. Conclusion Thiazolidinediones combined with metformin can greatly improve of insulin resistance and ovulation rates in PCOS women; besides, it is comparatively safe.