Peptic ulcer is involved with Helicobacter pylori infection and antibiotic regimens are primary treatments. An optimal therapeutic regimen for eradication of Helicobacter pylori remains uncertain due to variable efficacy. The objectives of this study were to evaluate the efficacy of omeprazole based antibiotic regimens in bacterial eradication, healing of peptic ulcer and to identify factors affecting efficacy. Seventy-seven patients were enrolled in the prospective, open-trial from November 1997 to Setember 1998. H. pylori infection was identified with endoscopy, H. pylori stain and rapid urease test. The first group (OAC7) received omeprazole 20 mg twice daily for 4 weeks which were the same schedule for all, amoxicillin and clarithromycin 500 mg three times daily for 1 week; the second group (OAC14), for 2 weeks on the same regimen as the first; and the last group (OACD) has taken bismuth in addition to the OAC7 regimen for 1 week. Eradication of H. pylori and healing of peptic ulcer were evaluated with endoscopy and tests for H. pylori before and after treatments. There were no significant differences in eradication rates; 77% in OAC7, 76% in OAC14, 81% in OACD (p=0.935) and healing rates; 82% in OAC7, 71% in OAC14, 95% in OACD (p=0.179), respectively. Compliance had an relationship with eradication rates significantly among regimens (p=0.049). Twenty three cases (29%) complained of the minor side effects. In conclusion, OAC7 was better in convenience of dosing schedule and showed fewer side effects with shorter duration and lower cost while There were no significant differences in efficacy among regimens.