AIM: To investigate the efficacy and tolerability of Hpylori eradication in an omeprazole-based triple therapy with high- and low-dose of clarithromycin and amoxicillin.METHODS: One hundred and sixty H pylori positive patients were randomly assigned to two groups based on the following 2 wk investigation; (1) group A or low-dose regimen received omeprazole 20 mg b.i.d, clarithromycin 250 mg b.i.d and amoxicillin 500 mg b.i.d; and (2) group B or high-dose regimen received omeprazole 20 mg b.i.d, clarithromycin 500 mg b.i.d and amoxicillin 1000 mg b.i.d. During the study H pylori status was assessed by histology and rapid urease test prior and by 13C-urea breath test 6 wk after the therapy. Standard questionnaires were administered to determine the compliance to treatment and possible adverse events of therapy. Data were subject to % to compare the eradication rates in the two groups. The significant level of 95% (P≤0.05) was considered statistically different.RESULTS: We found that the per-protocol eradication rate was 88% (68/77) in group A, and 89% (67/75) in group B. The intension-to-treat eradication rate was 85% (68/80) in group A and 83.75% (67/80) in group B. Overall adverse events were 26% in group A and 31% in group B. The adverse events were generally mild in nature and tolerated well in both groups with a compliance of 98% in group A vs 96% in group B.CONCLUSION: The omeprazole-based low dose regimen of clarithromycin and amoxicillin for two weeks in H pylori eradication is as effective as high dose regimen in Iranian population.