We report a case of a 79-year-old man who developed severe therapy-related pancytopenia from tegafur uracil(UFT)and Leucovorin(LV)as adjuvant chemotherapy for ascending colon cancer. Laparoscopic right hemicolectomy resection was performed for the ascending colon cancer. Pathohistological analysis revealed that the ascending colon tumor was moderately differentiated tubular adenocarcinoma(T3, N1, M0, and Stage III a). Postoperative adjuvant chemotherapy with UFT and LV was administered. After 2 courses of chemotherapies, severe thrombocytopenia(Grade 4)and neutropenia(Grade 4)were noted. Platelet and granulocyte-colony stimulating factor(G-CSF)were transfused. Furthermore, red blood cell transfusions were given for anemia(Grade 3). Dihydropyrimidine dehydrogenase(DPD)deficiency was suspected as the cause of the pancytopenia, and the ratio of dihydrouracil(DHU)and uracil(URA)was measured. However, the result was negative for DPD deficiency. Bone marrowaspiration revealed that therapy-related leukemia(TRL)and therapy-related myelodysplastic syndrome(T-MDS)were not the causes of the pancytopenia either. A total of 230 units of platelet transfusions and 20 units of red blood cell transfusions have been given for 32 weeks, and the patient currently requires routine blood transfusions. Fortunately, infection and bleeding never occurred. Subsequently, the patient should be monitored carefully.