Abstract: Objective :To present the clinic characteristics of thymoma and thymoma with myasthenia gravis (MG). Methods :Between 1975 and 2003,318 cases of patients with thymoma (181 cases of thymus tumor,137 cases of thymus tumor with myasthenia gravis) were surgically treated.Among the patients,181 cases of thymus tumor (TT, Group I ) were compared to 137 cases of thymus tumor with myasthenia gravis (TTMG,Group Ⅱ). Results :The average age for the patients in group I was 36.2, the youngest was 4 years old and the patients with diameter of tumors over 5cm accounted for 93.4%, and most of them (65.7%) were in the stage Ⅲ and Ⅳ of clinical pathology, the rate of operative resectability was 66.9%. In group Ⅱ, the average age was 46.2, the youngest was 20 years old and the patients with the diameter of tumor under 5cm accounted for 67.9%, among which 59.8% were in the stage I of clinical pathology, the rate of operative respectability was 86.1%. Conclusion :The diagnostic standard of thymoma at early stage is that the diameter of tumor is below 3 cm.The clinical characteristics of TTMG includes the short history, the fast progress and serious of MG symptoms, the high incidence of thymus-crisis at postoperative.