Repair of using the double patch method was performed on a 6-month old child with Down's syndrome. However, at 1 year and 4 months (BW: 3.6 kg), the patient's resulting mitral regurgitation became severe and clinically unmanageable, necessitating further operation. At operation the anterior leaflet of the mitral valve was lifted up at the anterolateral side due to the patch attached to the interventricular septum, which restricted the valve from closing completely. Moreover, secondary severe hardening of the valve tissue made it difficult to reconstruct the valve. Since the diameter of the valve was only 13 mm after resection, making the impossible use of a standard prosthetic valve, we constructed a new roll valve out of a heterologous pericardium. Almost no regurgitation was observed and prognosis was favorable although a pattern of mitral stenosis was observed. The patient died 6 months later due to the worsening of respiratory infection before a reoperation could be performed. Post mortem examination revealed comparatively good valve function except mitral stenosis due to inadequate valve size. This technique has practical application for mitral valve replacement of small valve annuli of infants when other methods are not feasible.