Objective: To improve positive rate of thymoma diagnosis. Methods: Antibodies to CAE (citric acid extract of human skeletal muscle ) were evaluated by Western blotting and ELISA respectively in sera of myastheni a gr avis patients (16 cases with and 17 cases without thymoma),normal adults(10 case s) and other disease patients (18 cases). Results: The rates of CA E-Abs to 3.4×104, 5.0×104, 6.0×104 ingredients of CAE-antigen in MGT patients were 93.7%(15/16),75.0%(12/16), 75.0%(12/16) r espect ively. None of other groups was binding to each of these 3 ingredients. The posi tive rates of MGT patients were 16/16,12/16 respectively. The false positive rat e s were 0/17,1/17 respectively. Conclusion: Western blotting assay was more sensitive and specific than ELISA in evaluating CAE-Abs.But the operation of Western blotting assay is more complicated and expensive than ELISA.