This study was a comparison of 1-week and 2-week triple therapies with omeprazole, amoxicillin, and clarithromycin (OAC) in patients with peptic ulcer disease and Helicobacter pylori infection. A total of 147 peptic ulcer patients with H. pylori infection assessed by histology and culture were randomly treated with omeprazole 20mg bid + amoxicillin 1000mg bid + clarithromycin 400mg bid for either 1 week (OAC1w) or 2 weeks (OAC2w). Both groups then received omeprazole 20mg daily for 2 weeks followed by ranitidine 300mg daily for 4 weeks. Eradication of H. pylori was assessed by histology, culture, and the 13C-urea breath test (13C-UBT) at least 6 weeks after cessation of antimicrobial therapy. Intention-to-treat eradication rates were 78.2% (95%CI 69%-87%) with OAC1w and 88.4% (95%CI 81%-96%) with OAC2w. Per-protocol eradication rates were 86.0% (95%CI 78%-94%) with OAC1w, 97.0% (95%CI 93%-100%) with OAC2w. There was no significant difference in the eradication rates between OAC1w and OAC2w. Side effects were mild and self-limiting in both groups. In conclusion, both 1- and 2-week triple therapy with OAC are well tolerated and provide good eradication rates in peptic ulcer patients in Japan. The eradication rate of the 2-week regimen was higher than that of the 1-week regimen, but the difference was not statistically significant. Further studies including long-term economic considerations are required to determine the optimal duration of treatment.