Abstract: Cathepsin B is a lysosomal cysteine proteinase that has the ability tO degrade severalextracellular matrix component and has been implicated in the progression of several human and rodent tumors. The purpose of this study was to investigate the expression ofCathepsin B in human gastric carcionma tissue. We have studied the expression ofCathepsin B in 55 surgical resection samples of gastric carcinoma by using monospecificpolyclonal rabbit antibody raised against human liver CB for immunohistichemistry. Theresults are shown over expression of Cathepsin B in gastric carcionoma when comparedwith normal gastric tissue. The increased staining of CB in malignant cells was associatedwith the depth of the invasiveness and the growth pattern as well as the metastasis of thelymph nodes, but not with the histological classification. Statistical differences are significant (P＜0.05 ). Inconclusion,our results indicate that the expression of CB in gastriccarcinoma correlates with tumor progression, and contributes to the development of theinvasive phenotype.