Several reports have described that the prognosis of patients with mitral valve regurgitation due to active infective endocarditis (IE) is better after mitral valve plasty (MVP) than replacement (MVR). However, extensive destruction of valve tissue might cause difficulties with MVP. We repaired a widely-affected anterior mitral leaflet (AML) using an autologous pericardial patch. A 44-year-old woman with mitral regurgitation presented with prolonged fever and backache. We made a diagnosis of active IE accompanied by mitral valve regurgitation. We performed MVP, widely resected the infected areas of the AML, and reconstructed the defective area using the pericardial patch. She was discharged after four weeks of antibiotic therapy, when she was free of recurrence. The pericardial patch facilitated MVP and was effective for treating mitral valve regurgitation due to active IE.