TS-1 is a new, oral anticancer agent composed of two modulators, gimeracil (CDHP) and oteracil potassium (Oxo) are mixed with tegafur in a ratio of 1:0.4:1. We report one case of advanced gastric cancer with lung and lymph node metastases that completely responded to TS-1. A 71-year-old woman was admitted to our hospital because of breathlessness. A diagnosis of advanced gastric cancer with extensive lymph node metastases and multiple pulmonary metastases was made. One hundred mg/body/day of TS-1 was orally administrated for 4 weeks. A partial response (PR) was obtained after the first course with regression of multiple pulmonary metastases. After 1 drug-free week, the second course was administered with 120 mg/body/day of TS-1 for 4 weeks. After two courses, the primary tumor was reduced to an ulcer scar with pathological confirmation of a complete disappearance of the cancer tissue. Moreover, computed tomography (CT) showed a complete regression of the extensive lymph node and diffuse lung metastases, for a complete response (CR). The serum level of CEA was reduced from 172.7 ng/ml to 8.1 ng/ml after TS-1 treatment. As for adverse events, only pigmentation of the skin and Grade 2 oral aphta were observed.