Imatinib mesylate has dramatically improved the outcome of children with Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph* ALL) and is now included as first-line therapy. Uncommon adverse effects of this drug for pediatric use, however, are largely unknown. We report the first case of a 9-year-old child who developed severe acute hepatitis with grade 4 transaminases and bilirubin elevation during imatinib treatment for Ph* ALL. Liver biopsy showed extensive lobular and pericentral necrosis of hepatocytes. Liver function recovered after discontinuing imatinib with a 4-week prednisolone. Extensive hepatic necrosis should be considered not only in adults but also in children under imatinib administration.