The purpose of this study was to investigate the correlation between efficacy and dose intensity of postoperative adjuvant chemotherapy with MMC and UFT. A total of 1,410 patients from 180 institutions were allocated into a low-dose group and a high-dose group. The patients in the low-dose group received MMC at 8 mg/m2 on the day of surgery and 3 capsules of UFT (300 mg in tegafur) daily for 6 months. The patients in the high-dose group received MMC at 8 mg/m2 on the day of surgery, and in weeks 4, 10, 16, and 22 after surgery and 6 capsules of UFT (600 mg in tegafur) daily for 6 months. The patients in the high-dose group tended to exhibit higher survival rates than those in the low-dose group, although the difference was not significant. For the n(+)ps(-) patients, however, the survival rates were significantly higher in the high-dose group (p = 0.043). The recurrence-free rates showed a similar tendency. The incidence rates of adverse events were significantly higher in the high-dose group than in the low-dose group. Compliance was poorer in the high-dose group. Although the number of adverse events increases, a better prognosis can be expected with a high dose. These results confirmed a dose-dependency in adjuvant chemotherapy with MMC and UFT.