Purpose: When cancer cels invade the stroma, they should be dissociated from the adjacent cells at first. E-cadherin and $eta-catenin$ constitute an important protein complex associated with cellular adhesion, development, and differentiation, especially in epithelial cells. The role of E-cadherin and $eta-catenin$ in gastric carcinogenesis were studied. Materials and Methods: The expression of E-cadherin and $eta-catenin$ in gastric adenocarcinomas by using immunohistochemical staining and the mutation by using polymerase chain reaction- single stranded conformation polymorphism (PCR-SSCP) and sequencing were performed in 40 adenocarcinomas and 5 dysplasia of stomach. Thirteen cases, which had lymph node metastasis, were also included for immunohistochemical staining. Results: Inappropriate cytoplasmic and/or nuclear expression of a E-cadherin-$eta-catenin$ complex was more frequent in poorly differentiated, diffuse type signet ring cell carcinomas than in well-differentiated, intestinal type adenocarcinomas (P<0.05). However, the expression was not related with clinical stage or lymph node metastasis. Mutation of E-cadherin was detected in 4 cases by using PCR-SSCP, whereas mutation of $eta-catenin$ was detected in 2 cases. Conclusion: E-cadherin and $eta-catenin$ seem to be important in gastric carcinogenesis, especially in poorly differentiated diffuse type.