Postoperative adjuvant chemotherapy with S-1 is a standard treatment for several digestive cancers. We conducted alter- nate-day oral therapy as postoperative adjuvant chemotherapy with S-1, for 31 patients with pathological stage II / IIIgastric cancer for whom radical resection had been performed. We examined the effects, the rate of compliance with all of the dosing instructions, cancer recurrence, and the survival rate with S-1 by the administration method for 31 cases. Twenty-eight patients(90. 3%)could be administered S-1 for one year. Those with side effects were admitted in 4 cases(13%). Those with side effects of grade 3 or more were not admitted. The 3-year survival rate was obtained; stage II 91%, and stage III 67% in gastric cancer. Four patients had recurrences at; the rate of 13%. In conclusion, the number of side effects was decreased, and a high rate of compliance with all dosing instructions was achieved in alternate-day oral therapy with S-1, compared with the daily oral method. This method can be a safe and useful way to administer S-1 oral therapy.