L-asparaginase (L-Asp) is a useful antileukemic agent for acute lymphoblastic leukemia (ALL); however, it often causes severe liver injury with marked fatty liver. Here, we present a case of L-Asp-induced fatty liver disease in a 21-year-old female patient with ALL. Serum cholinesterase levels, which are usually elevated in fatty liver, decrease at the onset of liver injury. After treatment with L-carnitine and vitamin B complex, the liver injury rapidly improved, resulting in the patient being able to continue subsequent chemotherapy.