Objective:Many studies reported that matrix metalloproteinase-9(MMP-9)participated in the development of esophageal squamous cell carcinoma(ESCC)and resulted in poor prognosis,however,they all included few patients and had inconsistent results.So we conducted a meta-analysis to explore the correlation between overexpression of MMP-9 and the clinicopathological characteristics and overall survival(OS)of ESCC.Methods:PubMed,EMBASE,Web of Science,Chinese Biomedical Literature Database,Google Scholar and other databases were searched for relevant studies.The Newcastle-Ottawa quality assessment scale was used to assess the methodological quality of included study and RevMan 5.2 software was used to conduct meta-analysis.Results:A total of 35 studies were included,and the results of meta-analysis showed that overexpression of MMP-9 was associated with grade of differentiation[well/moderate vs.poor:odds ratio(OR):0.39,95%confidence interval(CI):0.29-0.52;P<0.00001],lymph node metastasis(negative vs.positive:OR:0.24,95%CI:0.16-0.34;P<0.00001),TNM stage(T1/T2 vs.T3/T4:OR:0.28,95%CI:0.14-0.54;P=0.0002),the depth of invasion(T1/T2 vs.T3/T4:OR:0.29,95%CI:0.17-0.49;P<0.00001),and vascular invasion of ESCC(negative vs.positive:OR:0.35,95%CI:0.21-0.58;P<0.0001),and also associated with poor overall survival of ESCC(HR:2.17,95%CI:1.32-3.57;P=0.002).Subgroup analysis showed that more than 10%of carcinoma cell staining was associated with significant increase of mortality risk(HR:2.44,95%CI:1.16-5.15;P=0.02),and sensitive analysis suggested that MMP-9 was an independent prognostic factor in ESCC(HR:1.49,95%CI:1.16-1.91;P=0.002).Conclusions:On the basis of limited evidence,overexpression of MMP-9 may be a potential independent prognosis factor of ESCC patients in Asia,and high-quality studies assessing the prognostic significance of MMP-9 for ESCC patients are still needed. Many studies reported that matrix metalloproteinase-9 (MMP-9) participated in the development of esophageal squamous cell carcinoma (ESCC) and resulted in poor prognosis, however, they all included few patients and had inconsistent results. So we conducted a meta -analysis to explore the correlation between overexpression of MMP-9 and the clinicopathological characteristics and overall survival (OS) of ESCC. Methods: PubMed, EMBASE, Web of Science, Chinese Biomedical Literature Database, Google Scholar and other databases were searched for relevant studies The Newcastle-Ottawa quality assessment scale was used to assess the methodological quality of included study and RevMan 5.2 software was used to conduct meta-analysis. Results: A total of 35 studies were included, and the results of meta-analysis showed that overexpression of well-moderate vs. poor: odds ratio (OR): 0.39, 95% confidence interval (CI): 0.29-0.52; P <0.00001], lymph node metastasis TNM stage (T1 / T2 vs. T3 / T4: OR: 0.28, 95% CI: 0.14-0.54; P = 0.0002) , the depth of invasion (T1 / T2 vs. T3 / T4: OR: 0.29, 95% CI: 0.17-0.49; P <0.00001), and vascular invasion of ESCC : 0.21-0.58; P <0.0001), and also associated with poor overall survival of ESCC (HR: 2.17, 95% CI: 1.32-3.57; P = 0.002). Subgroup analysis showed that more than 10% of carcinoma cell staining was associated with a significant increase of mortality risk (HR: 2.44, 95% CI: 1.16-5.15; P = 0.02), and sensitive analysis suggested that MMP-9 was an independent prognostic factor in ESCC -1.91; P = 0.002) .Conclusions: On the basis of limited evidence, overexpression of MMP-9 may be a potential independent prognostic factor of ESCC patients in Asia, and high-quality studies assessing the prognostic significance of MMP-9 for ESCC patients are still needed.