Background. Therapy for relapsed or refractory (r/r) T-cell acute lymphoblastic leukemia (T-ALL) and T-cell lymphoblastic lymphoma (T-LBL) in children is challenging, and new treatment methods are needed. Previous studies have shown a promising response to the addition of nelarabine to chemotherapy for r/r T-ALL and T-LBL. Methods. We retrospectively analyzed the therapy of nelarabine in combination with etoposide, cyclophosphamide, and intrathecal therapy in eight pediatric patients with r/r T-ALL and T-LBL. The treatment regimen consisted of five consecutive days each of nelarabine (650mg/m ²/dose) and etoposide (100mg/m ²/dose)/cyclophosphamide (440mg/m ²/dose) separated by at least three days. Results. Five patients had T-ALL, and three patients had T-LBL. Of all patients, five achieved complete response, and the other three achieved partial response. All the patients underwent hematopoietic stem cell transplantation (HSCT) after two cycles of the treatment, except for one case with one course. Three patients who had previously received HSCT were treated with reduced-intensity conditioning regimens, including fludarabine, melphalan, and nelarabine; one of whom is still alive over five years after the second HSCT. Grade 2 neuropathy occurred in one patient, and other severe toxicities commonly associated with nelarabine were not observed during nelarabine-containing salvage therapy. With a median follow-up of 900 days for survivors, the 2-year overall survival and event-free survival rates were 60.0% and 36.5%, respectively. Conclusion. The addition of nelarabine to reinduction chemotherapy was useful for HSCT in remission and did not lead to excessive toxicity. In addition, a conditioning regimen including nelarabine appeared to be effective in previous HSCT patients.