TS-1 is an oral anticancer drug approved in Japan consisting of tegafur (a pro-drug of fluorouracil, 5-FU), gimeracil and oteracil potassium. The response rate of TS-1 in the untreated advanced gastric cancer patients was 44.6% in the late phase II study. In 2007, efficacy of the adjuvant therapy using TS-1 in the resected gastric cancer patients was demonstrated by ACTS-GC study group conducted in Japan. PSK is an oral anticancer drug approved in Japan consisting of protein-bound polysaccharide extracted from mycelium of Trametes (Coriolus) versicolor, a kind of mushroom. Even though survival benefit by PSK in combination with adjuvant chemotherapy using 5-FU or tegafur in the postoperative gastric cancer patients was already demonstrated, it is not uncertain about efficacy of combination therapy with PSK and TS-1 in gastric cancer. In this study, we compare efficacy and safety of postoperative adjuvant therapy using TS-1 or TS-1+PSK in the stage II or III gastric cancer patients.