We report the development of spinal infarction during adjuvant chemotherapy with tegafur, gimeracil and oteracil (TS-1) after surgery for lung adenocarcinoma. A 69-year-old female had a left upper lobectomy for pulmonary adenocarcinoma, T2aN0M0. Six weeks after the surgery, tegafur, gimeracil and oteracil were administered orally as adjuvant chemotherapy for 1 year. After 10 months of adjuvant chemotherapy, the patient suddenly showed signs of numbness and weakness in both lower limbs. The patient did not have a previous medical history, and was receiving only tegafur, gimeracil and oteracil with the stomach medication. Neurological findings showed muscle weakness, numbness and a loss of tendon reflex in both lower limbs, as well as bladder and rectal disturbance. Blood tests, brain magnetic resonance imaging and chest computed tomography showed no signs of abnormalities or metastasis. Magnetic resonance imaging of the spine showed a hyperintense lesion between the Th12 and L1 spinal levels by T2-weighted image. A spinal fluid test indicated no abnormalities, and cytological diagnosis was class II. Anti-aquaporin 4, anti-ganglioside and anti-neuronal autoantibodies were all negative. These results indicated that the patient had a spinal infarction, rather than myelitis or paraneoplastic neurological syndrome. The patient was treated with heparin and steroid pulse treatment followed by rehabilitation, and recovered sufficiently to be able to walk using a cane after 2 months. The development of spinal infarction during anti-cancer chemotherapy has not been previously reported. In this case, an association of spinal infarction with the use of adjuvant chemotherapy was strongly indicated due to the lack of abnormalities in coagulability, atherosclerotic lesions and aortic disease.