Matrix metalloproteinase-21 (MMP-21) has been shown to enhance tumor invasion and metastasis ability in some solid tumors. In the present study, we investigated the expression of MMP-21 as well as its association with overall survival of gastric cancer patients. MMP-21 expression was investigated in 296 cases of gastric cancer by immunohistochemistry assay. Statistical analysis was utilized to evaluate the association of MMP-21 expression with overall survival of patients. MMP-21 expression was proved to be increased in gastric cancer compared with that in normal tissues (P < 0.05). It was also proved MMP-21 expression was associated with tumor invasion, metastasis and TNM stage (P < 0.001). MMP-21 expression was showed to be associated with overall survival of gastric cancer patients for patients with tumor of higher MMP-21 expression tend to have worse overall survival (P < 0.001). Multivariate analysis proved MMP-21 to be an independent prognostic factor for overall survival of gastric cancer patients (P < 0.001). These results suggested the potential role of MMP-21 in progression of human gastric cancer. It might also be a novel molecular marker to predict overall survival of patients with gastric cancer.