u＞Introduction/u＞ Blinatumomab is a bispecific T-cell engager antibody construct targeting CD19 on B-cell lymphoblasts. The efficacy of blinatumomab has been reported in adult and pediatric acute lymphoblastic leukemia (ALL) and adult lymphoma, recently. To investigate the treatment response and toxicity, we retrospectively reviewed pediatric ALL cases treated with blinatumomab in multiple Korean pediatric hospitals. u＞Patients and methods/u＞ Clinical data of the patients were collected from 6 Korean pediatric hospitals. Following data were collected; disease status at blinatumomab treatment, early treatment response after blinatumomab first cycle, treatment-related toxicity, continuing treatment, current disease status. u＞Results/u＞ Nine patients were treated with blinatumomab. Median age of the patients was 11.9 years (range, 1.0-23.0), and there were 4 boys and 5 girls. Blinatumomab was treated as 3rd regimen in 5 patients, 4th regimen in 2 patients, and 5th regimen in 2 patients. Two patients were treated with fixed dose (9mcg/day, 1 week followed by 28mcg/day, 3 weeks), and others were treated with calculated dose of 5 mcg/m2/day for 1 week followed by 15mcg/m2/day for 3 weeks. One patient was treated 2 cycles of blinatumomab, and other 8 patients were treated once. Five patients (55.6%) achieved overall response after blinatumomab including three patients with molecular response, and two of the responders were treated with HSCT. Responders showed spontaneous platelet recovery at the end of blinatumomab infusion. There was one patient who discontinued treatment because of no response with aggravating leukocytosis. Seven patients (77.8%) experienced cytokine release syndrome (two grade 2, four grade 1). Three cases were observed neurotoxicity, which were seizure, involuntary movement, and headache. Grade 3 or 4 hematologic toxicities were observed in all patients. One patient experienced repetitive ventricular tachycardia lasting few seconds, which recovered after completion of blinatumomab. u＞Conclusion/u＞ Blinatumomab resulted in overall response in 55.6% of cases with 2 or more leukemia relapses. Toxicity of blinatumomab was tolerable, and there was no treatment-limiting toxicity. Blinatumomab can be an effective treatment for relapsed/refractory pediatric ALL patients with tolerable toxicity.