Objective: To investigate the significance of abnormal E-cadherin and β-catenin expression in pancreatic intraepithelial neoplasia (PanIN) and pancreatic adenocarcinoma. Methods:Pancreatic samples of 156 cases were retrospectively studied from surgery and autopsy in Changhai hospital from January 2001 to December 2003, from which tissue microarray blocks containing 129 PanIN-1A lesions, 104 PanIN-1B lesions, 22 PanIN-2 lesions, 11 PanIN-3 lesions, and 121 pancreatic ductal adenocarcinomas and corresponding paracancerous tissues were constructed. EnVision method of immunohistochemistry was used to detect the E-cadherin and β-catenin expression. The correlation between the abnormal E-cadherin and β-catenin expression and clinicopathological parameters was analysed. Results: The rate of E-cadherin abnormal expression was significant in ductal adenocarcinomas compared with the PanIN lesions and normal ducts(64.5%,32.3%,0%), moreover, the rate of E-cadherin abnormal expression was in relation to differentiation, lymph node metastasis and perineural invasion of pancreatic adenocarcinoma(P<0.05). There was remarkable increase in the E-cadherin cytoplasmic expression in PanIN lesions and ductal adenocarcinomas compared with normal ducts. The rate of β-catenin abnormal expression was found to be related with lymph node metastasis and perineural invasion of pancreatic adenocarcinoma(P<0.05). The expression of β-catenin cytoplasm and/or nucleus was significant in high-grade PanIN lesions and ductal adenocarcinomas compared with low grade PanIN lesions or normal ducts(P<0.05). There was a positive relationship between the E-cadherin and β-catenin expression in PanIN lesions and ductal adenocarcinomas (P<0.01, P<0.05). Conclusion: There is aberration in the expression of the E-cadherin and β-catenin in PanIN lesions and ductal adenocarcinomas, suggesting the E-cadherin and β-catenin changes is not only related with the biological action and prognosis, but also involved in pancreatic carcinogenesis.