Abstract: Objective: To investigate the expression and significance of E-cadherin and β-catenin in the invasion and metastasis of thymoma. Methods: β-catenin and E-cadherin monoclonal antibody was used to examined thymic epithelial tumor tissue paraffin sections of 87 cases by the method of immunohistochemistry PV-6000 and the relationship between the expression and the invasion and metastasis of thymoma was observed. Results The expression of E-cadherin and β-catenin in the classification of thymoma according to WHO and Masaoka: The expression of E-cadherin in epithelial thymoma, and the expression in A, AB, B1, B2, B3 and C were 44.4%, 37.5%, 41.2%, 47.1%, 58.3% and 31.3%, respectively. There was no statistically significance between the difference. (χ2 = 2.394, P> 0.05). According to the Masaoka system stage I, II and III-IV, the positive expression rate was decreased with the increase of tumor stage and the rates were 60%, 19.2% and 18.2% respectively. The difference between the two groups was statistically significant (χ2 = 15.469, P <0.05). The expression of β-catenin in thymoma: The expression in WHO type A, AB, B1, B2, B3 and C were 33.3%, 25%, 29.4%, 23.5% and 33.3% and 37.5%, respectively. The difference was not statistically significant (χ2 = 1.074, P> 0.05). The positive expression rates of Masaoka system in stages I, II and III-IV with the increase of tumor staging were 37.5%, 76.9% and 90.9%, respectively. The differences between the two groups were statistically significant (χ2 = 24.625, P <0.05)