Seizure is one of the most frequent neurological complication and morbid phenomenon among children receiving chemotherapy for acute lymphoblastic leukemia. As overall survival of children with acute lymphoblastic leukemia is improving, now the challenge is to reduce treatment-related adverse effect. However, not much is known about the etiology and natural history of these seizure in our pediatric population. This is a single centered study conducted in the Department of Pediatric Hematology and Oncology, Bangabandhu Sheikh Mujib Medical University. This prospective observational study was conducted over a period of 1 year from May 2017 to April 2018. A total of 105 patients aged 1 year to 17.9 years newly diagnosed as acute lymphoblastic leukemia were the study population. This study showed that in five (33.3%) patients, the underlying cause was suspected intracranial hemorrhage and it was the most common cause. All these five patients had features of severe sepsis and upper motor neuron sign associated with severe thrombocytopenia. Among them three had coagulopathy. Three (20%) patients had CNS leukemic infiltration. Suspected meningitis was attributed as the possible cause of seizure in two (13.33%) patients. Other identifiable causes were brain abscess in one patient, multiple cerebral infarction in one patient, hypertensive encephalopathy in one patient, and vincristine-induced neurotoxicity in one patient. In one patient no identifiable cause was found. Among 15 patients with seizure five (33.3%) patients were improved and completed induction remission chemotherapy. Ten (66.7%) patients died. In this study, we found sepsis and coagulopathy as the major underlying cause of seizure. Outcome was found very dismal in patients who developed seizure.