We report a case of unresectable gastric cancer, who had been treated with S-1 alone for 3 years without cancerous symptoms. The patient was a 66-year-old male. His diagnosis was advanced gastric cancer based on gastrofiberscopy. He underwent surgery on April 15, 2003. The tumor proved to be unresectable due to direct invasion of the pancreatic head, so only gastrojejunostomy was performed. On day 14 after surgery, the administration of S-1 alone was commenced at a dose of 100 mg per day in a 4-week course of medication at 2-week intervals. No side effects were noted. Moreover, his quality of life (QOL) was not disturbed, and he led an active social life throughout the course. Long survival was achieved by S-1 alone.