A patient, 68-year-old female, underwent open mitral commissurotomy (OMC) for rheumatic mitral stenosis in April, 1979. In July of 1992, during the postoperative follow-up echocardiogram showed 8 x 7 mm mitral subvalvular tumor mass and mitral restenosis. Then, mitral valve replacement was performed using prosthetic valve (Carbomedics #25 mm). The tumor was located on the top of postero-medial papillary muscle and its chordae, and histologically was diagnosed as benign papillary fibroelastoma. Based on the findings of periodic echocardiogram, the tumor doubling time was estimated to be 283 days. The postoperative course was uncomplicated and she was discharged on the 34th post operative day. Papillary fibroelastoma is a rare benign cardiac tumor. Pathological origin of this tumor is still unknown. However, Lambl's excrescence, long-term inflammatory stimulation and/or thrombi are supposed to be etiologic factors. This tumor is generally found incidentally at the time of autopsy or operation because the patients are often asymptomatic. However, because the tumor causes embolism at times, periodic examination by echocardiogram after operation preserving valves is recommended, and surgical resection is required when the diagnosis is established.