To investigate the diagnostic significance of SOX9 in thymic tumors, immunohistochemistry staining of SOX9 expression was performed in 34 thymomas (including 8 cases with type A, 6 with type AB, 6 with type B1, 9 with type B2, and 5 with type B3 thymomas) and 20 thymic carcinoma tissues. The gene discussed is SOX9; the disease is thymoma.