Abstract: Objective:To investigate the long-term efficacy of a conditioning regimen containing fludarabi -ne in allogeneic hematopoietic stem cell transplantation (allo-HSCT) for hematologic malignancies. Methods: Patients with acute myelogenous leukemia (n=3), acute lymphoblastic leukemia (n=5), chronic myelogenous leukemia ( n=6), and myelodysplastic syndrome ( n=1) received allo-HSCT between February 2003 and De-cember 2004. There were 6 HLA-identical sibling donors, 8 family partially mismatched donors and 1 unrelat-ed donor. The conditioning regimen consisted of fludarabine (Flu30mg/m 2 ·d for5 days), busulfan (BU 4mg/ kg·d for3 days) and cyclophosphamide (CTX 50mg/kg·d for2 days). Ara-C (1.0~2.0g/m 2 ·d for2 days) was added in 8 patients and rabbit anti-T-lymphocyte globulin (3.0～5.0mg/kg.d for3 days) was added in 9 HLA-mismatched and unrelated patients. All patients received cyclosporine, short-term methotrexate and my-cophenolate mofetil for prophylaxis of graft-versus-host disease (GVHD). The 5-year overall survival rates were analyzed by Kaplan-Meier method.Results: All of the patients were successfully engrafted, with no se-vere regimen-related toxicity. The incidence of acute GVHD and chronic GVHD was 33.3% and 85.7% , re-spectively. Shingles occurred in7.1% of the patients. The 5-year overall survival (OS) was 53.3% for all of the patients. The 11patients who received transplantation during the first CR or chronic phase had higher overall survival rate than the 4 patients who received transplantation in the second CR, relapse, accelerated phase or blastic phase (72.7% versus0, P=0.0003). The main causes of death were relapse and GVHD. Conclusion:Al -lo-HSCT following a fludarabine-based reduced intensity conditioning regimen is an effective option for pa -tients transplanted in the first CR or chronic phase. This type of treatment plan has a low relapse rate and does not increase extramedullary toxicity or the infection rate. For the patients transplanted in the first CR or chronic phase, addition of fludarabine to the conditioning regimen has no effect on GVHD in allo-HSCT.