Metformin has been reported to have anticancer effect and can affect patient survival in several malignancies. However, the results are inconclusive for endometrial cancer. Hence, we conducted a systematic review and meta-analysis to investigate the prognostic role of metformin in patients with endometrial cancer. Studies were identified from Pubmed and Embase database through March 2017. Observational studies reporting hazard ratios (HRs) with 95% confidence intervals (CIs) for overall survival (OS) and progression-free survival (PFS) were selected. Data were abstracted and summarised using random-effects models. From 250 unique citations, we identified ten studies including 6242 patients with nine studies examining OS and five studies examining PFS. Meta-analysis demonstrated that metformin users had better OS (HR, 0.58; 95% CI, 0.45 to 0.76; P = 0.207, I-2 = 26.6%) and PFS (HR, 0.61; 95% CI, 0.49 to 0.76; P = 0.768, I-2 = 0%) than non-users for endometrial cancer patients. Similar findings were observed using sensitivity analysis adjusted by trim and filled methods (HR, 0.47; 95% CI, 0.37 to 0.58) and subgroup analyses. Based on the current evidence, we find that metformin use is associated with better OS and PFS in patients with endometrial cancer. However, further large-scale prospective studies are needed to establish its validity.