A 75-years-old woman was presented with nonthymomatous myasthenia gravis. She was treated with anticholinesterase which did not improve her outcome. The clinical classification of the Myasthenia Gravis Foundation of America (MGFA) was IVa. Before thymectomy, her bulbar symptoms got worse, but rapid improvement was obtained by plasma exchange. She had undergone transsternal extended thymectomy and there was no critical event after thymectomy. She had been treated with prednisolone for 12 months and pharmacological remission was recorded.