We report a 49-year-old female patient with secondary myelodysplastic syndrome who developed liver dysfunction and acute renal failure caused by low-dose cytosine arabinoside (Ara-C) therapy. Treatment of low-dose Ara-C has widely been used for acute myelogeous leukemia and myelodysplastic syndrome, and it is thought to be a low toxicity except for myelosuppression. The patient complained of a transient adverse reaction in the second and third course of therapy. This rare case indicates that careful observation should be carried out during low-dose Ara-C therapy in view of allergic reactions.