Background: Pediatric patients with high risk or relapsed acute lymphoblastic leukemia (ALL) have worse prognosis than all other patients with ALL. Because outcomes were poor after treatment with chemotherapy only, patients with high risk of relapse have clear indications for allogeneic hematopoietic stem cell transplantation (HSCT). We report the outcomes of 36 children with relapsed ALL and very high risk ALL who received HSCT in Yeungnam region of Korea. Methods: From January 2004 to December 2013, children (up to age 18 years) with ALL who received HSCT (n=36) at Yeungnam region of Korea were reviewed retrospectively. Patients transplanted in the first complete remission (CR1, n=19) had very high-risk features, including high-risk chromosome translocation, white blood cell count at diagnosis exceeding 200,000/㎕, induction failure or others. Of the patients transplanted after relapse (CR2, n=17), most were in the second remission at HSCT. Results: Median age at transplantation was 6.75 years (range 0.92 – 14.25 years). Stem cell sources included 19 peripheral blood stem cells ( PBSC), 4 bone marrows (BM) and 13 umbilical cord bloods (CB). 7 patients received conditioning regimen including fractionated total body irradiation (TBI) with cyclophosphamide or melphalan and 26 patients received busulfan based conditioning regimens. The median infused CD34+ cells were 4.3 x 106/kg of BM and PBSC transplants (n=23) and 2.6 x 105/kg of CB transplants (n=13). All but 3 patients who received unrelated cord blood transplants showed successful engraftment. The median time to ANC recovery was 14 days (range 9-23 days). The incidence of acute GVHD was 50% including 15.6% of grade III-IV acute GVHD. Chronic GVHD developed in 8 of 29 (27.6%) evaluable patients. Patients who transplanted after CR2 suffered from significantly higher incidence of grade III-IV acute GVHD (5.9%) compared with CR1 (26.7%) (p=0.001). The estimated 5-year event-free survival rate (EFS) and overall survival (OS) were 69.4 ± 9.2%, 75.0 ± 8.5% respectively. The 5-yr EFS and OS were significantly higher in CR1 patients than in CR2 patients (p=0.045). The cumulative incidence of relapse in CR2 patients was 23.5%, but there was no relapse in CR1 patients. Conclusion: HSCT is effective treatment for pediatric patients with ALL who had very high-risk features in CR1 or already relapsed.