We performed this study to evaluate the therapeutic responses of bone marrow transplantation and immunosuppressive therapy for aplastic anemia in 103 cases (68 severe and 35 moderate). Among them, 15 cases with severe aplastic anemia having HLA-identical sibling donor underwent bone marrow transplantation, and cases(53 severe and 35 moderate cases)without available HLA-identical sibling donor had received immunosuppressive therapy using antilymphocye globulin and cyclosporin-A. The results were as follows; 1) For cases given bone marrow transplantation, successful engraftment was accomplished in all cases, but 2 cases showed rejection and 1 case died of thrombotic thrombocytopenic purpura (TTP), resulting 80% disease-free survival rate. acute graft-versus-host disease above grade II was noted in 2 cases and chronic graft-versus host disease was seen in other 2 cases. The most common pathogenic organism in post-transplantation infection was Herpes zoster (6 cases), and one each cases of Herpes simplex, candidiasis, measles and hemorrhagic cystitis developed. 2) Among 88 cases of receiving immunsouppressive therapy, complete response was seen in 26 cases (29.5%) and partial respones in 37 cases (42.0%), resulting 71.6% of overall response rate and recurrence rate was 19.5% (12 cases). In 53 severe cases, complete response was seen in 9 cases (17.0%) and partial response in 25 cases (47.2%), resulting 64.2% of overall response rate. In 35 moderate cases, complete response was seen in 17 cases (48.6%) and partial response in 12 cases(34.3%), overall response rate was 82.9%. All initial responses were seen within 6 months post-treatment period, and the time interval to initial response was 8 to 162 days (median; 53 days). There was no sex difference concerning response rate, however, partial response was predominant in male and more complete response in female. The complications of immunosuppressive therapy were thrombocytopenia (93.2%), fever (67.7%), hypertension (50.0%), skin eruption (45.8%), gingivitis (17.0%). In conclusion, our date suggest that bone marrow transplantation is preferred initial treatment modality to immunosuppressive therapy in severe aplastic anemia patient with HLA-identical sibling donor, and immunosuppression is a satisfactory alternative therapy for children with severe aplastic anemia in the absence of HLA-identical sibling and for whom with moderate aplastic anemia.