PURPOSE: The International Organization for Standardization-5fluorouracil (FU) 10 trial found that bolus 5-FU and l-leucovorin was not inferior to S-1 in the treatment of gastric cancer (GC). Continuous 5-FU and the rapid injection of 5-FU have different anti-cancer effects. Thus, bolus 5-FU and l-leucovorin treatment might be useful for oral FU-resistant GC. MATERIALS AND METHODS: We retrospectively analyzed the medical records of all patients with S-1 or capecitabine-resistant, unresectable, or recurrent GC treated with bolus 5-FU and l-leucovorin between January 2010 and December 2015 at Hokkaido University Hospital. The bolus 5-FU and l-leucovorin regimen consisted of intravenous l-leucovorin (250 mg/m²/2 h) and bolus 5-FU (600 mg/m²) administered once weekly followed by a 2-week rest period; each cycle was repeated every 8 weeks. RESULTS: A total of 14 patients were identified. The disease control rate was 35.7%. The median progression-free survival was 1.6 months (95% confidence interval [CI], 1.3~2.0 months), and the median overall survival was 6.3 months (95% CI, 4.7~7.9 months). No patient died from treatment-related causes. The most common severe adverse event associated with bolus 5-FU and l-leucovorin was neutropenia, which occurred in 21.4% of patients. CONCLUSIONS: Bolus 5-FU and l-leucovorin treatment might be useful for oral FU-resistant GC. We are planning a multi-center prospective phase II trial to evaluate the efficacy and safety of bolus 5-FU and l-leucovorin treatment for pre-treated unresectable or recurrent GC to confirm the results of this limited, retrospective study.