A 61-year-old male who noticed muscular weakness of his extremities, diplopia and slur his words was found to have a thymic tumor on computed tomography. The immunological examination showed incremental of anti Acetylcholine receptor antibody titer and anti P/Q-type voltage-gated calcium channels antibody titer. Electromyography showed decremental response to low frequency stimulations, and incremental response to high frequency stimulations. So he was diagnosed with thymic tumor combined with myasthenia gravis and Lambert-Eaton myasthenic syndrome. He treated with extended thymomectomy resulting in the improvement of his neurological symptoms. Five years after operation, the patient is well without any malignant diseases.