Surgical management of congenital mitral valve regurgitation (MR) is challenging, and the short- and long-term outcomes remain controversial. In this study, posterior leaflet extension using 0.625％ glutaraldehyde-treated autologous pericardium for 5 min was performed in two patients (aged 1 year and 4 months, and 5 months) with moderate MR through hypoplastic posterior leaflet of the mitral valve. There were no additional reparative procedures for the mitral valve. Shortly after surgery, MR was mild and none, respectively. Mid- and long-term assessments showed that MR was trivial and none, respectively, without increase in the peak velocity of the mitral valve. Posterior leaflet extension using glutaraldehyde-treated autologous pericardium is an attractive alternative for the treatment of MR with hypoplastic posterior leaflet of the mitral valve in pediatric patients.