To investigate the usefulness of oral doxifluridine (5'-DFUR), an active intermediate metabolite of capecitabine (XELODA), in gastric cancer patients after curative resection, we conducted a phase III randomized controlled study to compare oral 5'-DFUR and oral 5-fluorouracil (5-FU). 485 gastric cancer patients with Stage II or III operative findings at curative resection were registered and administered 5'-DFUR (460 mg/m2/day, daily, for two years) or 5-FU (115 mg/m2/day, daily, for the same period). Although no differences in overall survival or disease-free survival were detected, subset analysis showed 5'-DFUR was more effective in reducing peritoneal recurrence than 5-FU (p = 0.047), and in patients with Stage III or stage IIIb (histologic findings) in the 5'-DFUR group had more favorable disease-free survival curves and survival curves than the 5-FU group with similar stages.