We reported a successful mitral valve plasty for a 91-year-old woman with mitral valve prolapse. She has lived healthfully and independently without a big problem. She was admitted to another hospital for acute heart failure. Echo cardiography revealed prolapse of posterior mitral valve leaflet and severe mitral regurgitation. Drug therapy was not enough to control her complaint In spite of her age, the patient was able to support herself, and she and her family desired to have a surgical treatment. Therefore she referred to our hospital and underwent mitral valve plasty. Post operative course was almost uneventful. She discharged the hospital 3 months after the operation. If a selective criteria for individual patients is applied, the nonagenarian can safety undergo cardiac surgery.