We report a rare case of a 70-year-old woman diagnosed as having blepharospasm with positive anti-acetylcholine receptor antibody. Blepharospasm developed in November, 2000, and increased in frequency, and worsened toward the evening. She complained of difficulty in her eyelid opening from October, 2002. Neurological examinations revealed blepharospasm and mild ptosis in both eyes. Tensilon test was negative. Waning and waxing were not detected in bilateral orbicularis oculi muscles by Harvey-Masland test. However, anti-acetylcholine receptor antibody was positive and thymoma in the anterior mediastinum was also found by the computed tomography of the chest. After the thymectomy, frequency of blepharospasm decreased. When blepharospasm worsened toward the evening, the co-existence of myasthenia gravis should be borne in mind.