High-dose Busulfan in combination chemotherapy has been used commonly for hematopoietic stem cell transplantation. It crosses the blood-brain barrier and could cause seizure. Benzodiazepines have been used as anticonvulsant prophylaxis. This is a prospective study using oral lorazepam together with busulfan-based conditioning regimen in 30 children undergoing hematopoietic stem cell transplantation. The dose of lorazepam used ranged from 0.017 to 0.039 mg/kg (median = 0.026 mg/kg) per dose. None of the patients developed seizure while receiving oral lorazepam or within 72 hours of the last dose of Busulfan. Oral lorazepam was tolerated by the patients, but all patients needed dose reduction due to some adverse effects. In the authors' experience, oral lorazepam is a useful anticonvulsant prophylaxis for children receiving high-dose busulfan.