We report here a very rare case of chronic myeloid leukemia (CML) following long-term chemotherapy with 5'-deoxy-5-fluorouridine (5'-DFUR) for gastric cancer. A 69-year-old man was diagnosed with the chronic phase of CML. Six years previously, he underwent radical subtotal gastrectomy for gastric cancer, and was subsequently treated with oral anti-metabolite 5'-DFUR as adjuvant chemotherapy for 6 years. He was placed on imatinib therapy, and achieved a major molecular response 10 months after the initiation of therapy. This is the first reported case of therapy-related CML following 5'-DFUR treatment.