Malignant infantile osteopetrosis (MIOP) is characterized by a lack of osteoclastic function,with disturbed bone building and remodeling.1 Most children with this disease die within the first decade of life of secondary consequence of bone marrow failure.Hematopoietic stem cell transplantation(HSCT)is the only curative therapy for MIOP,an otherwise fatal disease.2 We present a girl wim MIOP who underwent a successful unrelated cord blood transplantation(CBT)in Taiwan,China.She was the first case from the mainland of Chinawho has come to Taiwan province for HSCT.