non-myeloablative BuCy+fludarabine conditioning regimen,and another one was treated with TBI+VP-1 6 +CTX+CCNU conditioning regimen.Only one case received short-term MTX,cyclosporin A and ATG regimen for prevention of graft-versus-host disease (GVHD).The GVHD prevention regimens of the other patients were based on short-term MTX,cyclosporin A,ATG and mycophenolate mofetil regimen.The hematopoietic reconstitution, complications and prognosis were observed.Results One patient died of intracranial hemorrhage,and hematopoi-etic reconstitution was achieved in the other 20 patients.The median time for hematopoietic reconstitution shortened by one day in large-dose group compared with that in low-dose group.Adverse reactions included high fever, shivering,gastrointestinal tract adverse reaction,liver injury,oral mucositis and other rare side effects.GVHD occurred more frequently in patients with HLA mismatched transplantation.Nine patients with aGVHD and 9 patients with cGVHD recovered after effective treatment.Within 100 days after transplantation,18 patients had bacterial or fungal infection,mainly upper respiratory tract infection;7 patients had cytomegalovirus infection;2 had EB viremia,and one had urinary BK virus infection.Only one patient died of VOD.Hemorrhagic cystitis occurred in 5 patients and improved after treatment.The median survival time was 24 months (ranging from 136 days to 9 years).One-year and 3-year overall survival rates were 85.2% and 63.9%,the disease free survival rates were 81% and 23.8%,recurrence free survival rates were 71.4% and 14.3%,respectively.Conclusion URD-HSCT was an effective method to treat leukemia.Conditioning regimen of BuCy and modified BuCy2 were safe and effective,the adverse reactions were reversible and well tolerated.Hematopoietic reconstitution time shortened in large-dose MNC and CD34 + cell number groups compared with that in low-dose group.The occurrence rate of GVHD with HLA mismatched transplantation was more than that of HLA matched transplantation.Low-dose heparin,prostaglandin E1 and Danshen injection can effectively prevent VOD.