A 31-year-old pregnant woman was referred to our hospital due to anemia and thrombocytopenia, and was diagnosed as having myelodysplastic syndrome (refractory anemia) with autoimmune thrombocytopenia. Administration of high dose methylprednisolone and gamma-globulin did not raise her platelet count, and she subsequently delivered a healthy baby after the transfusion of a large amount of platelets. Although the anemia spontaneously improved after delivery, the platelet count remained unchanged. Prednisolone was thus administered a second time, which did finally increase the platelet count. This is the first reported case of a pregnant woman with myelodysplastic syndrome in whom corticosteroid administration was effective for thrombocytopenia.