We herein report a case of ocular myasthenia gravis (MG) that was highly positive for anti-muscle-specific tyrosine kinase (MuSK) antibodies. The examined patient exhibited bilateral ptosis and lateral gaze palsy without any generalized symptoms and was diagnosed with ocular MG with anti-MuSK antibodies. She responded to treatment with prednisolone and immunosuppressants and experienced only ocular symptoms for four years and eight months after onset. Ocular MG with anti-MuSK antibodies lasting for a long term has rarely been described. Our findings suggest that it may be reasonable to test for the presence of anti-MuSK antibodies in patients who present with external ophthalmoplegia.