Matrix metalloproteinases (MMPs) play an important role in the extracellular matrix degradation, that is an essential step in tumor invasion and metastases. The current study objective was to evaluate the expression of MMP-9 in the neoplastic and in the interstitial inflammatory infiltrate cells in gastric cancer (GC). Moreover, the relationship between expression of this enzyme and clinicopathological features of GC, such as TNM stage, the depth of tumor invasion, lymph node and distant metastases were assessed. The study comprised 54 patients with gastric cancer. Immunohistochemistry was used to determine the expression of MMP-9 in gastric cancer cells. The semi-quantitative scale was applied to evaluate the expression of metalloproteinase-9. Immunohistochemical testing revealed a positive reaction of MMP-9 in 98% of all cancer tissue specimens and in 93% of inflammatory cells. The expression of MMP-9 in the neoplastic and inflammatory cells increased with more advance tumor stage, depth of tumor invasion and presence of lymph node as well as distant metastases. These findings indicate the significance of interstitial inflammatory infiltrate cells in the MMP-9 synthesis and the role of this enzyme in the invasiveness and metastatic potential of GC.