Objective: Matrix metalloproteinase-9(MMP-9) plays an important role in tumor cell invasion. Although it has been studied frequently in ovarian cancer, its prognostic impact is still equivocal. The aim of this study was to more precisely estimate its prognostic significance. Method:We searched Pubmed, Embase, OVID, Sciencedirect and CBM databases to identify eligible studies. Hazard ratios (HRs) or odds ratios (ORs) with 95% confidence intervals (95% CIs) were pooled across studies using fixed-effects or random-effects models. We also performed subgroup analysis. Results: 30 studies (n=2552 patients) focusing on prognosis or expression of MM-9 were included. Increased expression of MMP-9 was associated with poor prognosis in ovarian cancer patients (HR=1.68, 95%CI 1.09-2.59, p=0.02). Besides, MMP-9 expression in ovarian cancer was significantly higher than non-malignant tumors (OR=11.46, 95%CI 8.47-15.50, P<0.00001). Moreover, increased expression of MMP-9 was significantly associated with FIGO stage (OR=4.85, 95%CI 2.60-9.04, P<0.00001), grade of differentiation (OR=3.34, 95%CI 2.46-4.54, P<0.00001), lymph node metastasis (OR=5.75, 95%CI 3.71-8.92, P<0.00001) and there was no association with histological type of ovarian cancer. Conclusions: Increased expression of MMP-9 was associated with poor prognosis in ovarian cancer patients. Down-regulation of MMP-9 is an attractive therapeutic approach which might improve outcome of ovarian cancer.