A 65-year-old man was diagnosed with hypertrophic cardiomyopathy 11 years previously. Five years previously, he was hospitalized for pneumonia and heart failure and mitral regurgitation (MR) occurred due to systolic anterior motion (SAM) of the mitral valve. Two months previously, he was admitted for cardioembolic stroke, and echocardiography showed that SAM had disappeared. However, severe MR owing to posterior leaflet prolapse was observed. Mitral valvuloplasty, ventricular septal myectomy, pulmonary vein isolation, and left atrial appendage closure were performed. Postoperative echocardiography revealed no SAM and the patient was doing well. Here, we report a rare case of MR due to chordae rupture during follow-up of hypertrophic obstructive cardiomyopathy.