OBJECTIVE To observe whether benign and malignant gastric epithelial cells express cytotoxic protein GrB and investigate its effect on local immune response. METHODS Immunohistochemical staining for GrB was performed on paraffin sections from 8 specimens of chronic superficial gastritis (CSG) and 35 specimens of gastric cancer (GC) to detect the GrB expression and density of infiltration by GrB(+)cytotoxic lymphocyte (CTL) and NK. RESULTS (1) GrB was expressed in both benign and malignant gastric epithelial cells with the expression rates of 62.5% (5/8) and 40% (14/35) respectively (kappa(2) = 0.58, P > 0.05). (2) The density of infiltration by GrB(+) CTL and NK in GC group was greater than that in CSG group, however without significant difference (t = 1.628, P > 0.05). (3) The density of infiltration by GrB(+) CTL and NK, and GrB expression in GC showed no significant difference among different clinicopathological variables except age. The GrB expression rate in age group impended to the marked level of test (P = 0.06). (4) The density of infiltration by GrB(+) CTL and NK in GrB-positive GC group was significantly less than that in GrB-negative GC group (t = 1.89, P < 0.05). The density of infiltration by GrB(+) CTL and NK showed a significantly negative correlation with GrB expression in GC (gamma(s) = -0.55, P < 0.001). CONCLUSION GrB expression in gastric epithelial cell may be one of the accompanying changes in the course of malignant transformation of cells and play an important role in inhibiting local immune response, and it can be speculated as a novel molecule mechanism for tumor to escape immune surveillance.