Background: Helicobacter pylori (H. pylori) infection is important risk factors for chronic gastritis, peptic ulcer and gastric cancer. Bismuth-containing quadruple therapy has recently been the first-line regimen recommended in many European countries but has limited efficacy in ASEAN especially Thailand. This study was aim to evaluate efficacy of high dose PPI Bismuth-containing quadruple therapy with probiotics supplement for H. pylori eradication. Methods: In this double-blind randomized placebo-controlled study, H. pylori infected patients were randomized to receive 7-or 14-day high dose PPI- bismuth-containing quadruple therapy with or without probiotics supplement. Probiotic was 37.5 mg Lactobacillus reuteri (Biogaia®) in tablet twice daily. CYP2C19 genotyping and antibiotic susceptibility tests were also done. H. pylori eradication was defined as a negative 13C-urea breath test at least 4 weeks after treatment. Results: 100 subjects were enrolled (72 females, 28 males, mean age=54 years). Antibiotic resistance was 15.6% for clarithromycin, 34.1% for metronidazole. CYP2C19 genotyping was performed in both group and revealed 13%, 50% and 37% for poor, intermediate and rapid metabolizers, respectively. Overall eradication rates of 7-day and 14-day regimens with probiotic were 68% and 96%; P value=0.027. The eradication rate for all patients with poor and rapid metabolizers were 100% with 14-day regimen. 14-day regimen with probiotics can provide 100% eradication with clarithromycin resistance, metronidazole resistance or dual clarithromycin and metronidazole resistance group. Furthermore, the incidence of nausea and vomiting, abdominal discomfort, and bitter taste were significantly lower in patients with probiotics group compared with placebo (6%vs.26%, P=0.002,OR=0.126,95% CI=0.03-0.53; 4%vs.18.0%, P=0.017, OR= 0.155,95% CI=0.03-0.81 and 4%vs.26%, P= 0.001,OR= 0.08, 95%CI= 0.016-0.41, respectively). Conclusions: The 14-day high dose PPI- bismuth-containing quadruple therapy with probiotic can provide an excellent cure rate for H. pylori infection as first line treatment irrespective of CYP2C19 and antibiotic resistance pattern. Adding probiotic also significantly reduced treatment-related adverse events and improve the patients’ compliance.