Lansoprazole (LPZ), amoxicillin (AMPC) and clarithromycin (CAM) are commonly used drugs (LAC regimen) for Helicobacter pylori (H. pylori) eradication, but the eradication rate with this regimen was reported to be 70% to 90%. A few studies have reported that a successful eradication was associated with the CYP2C19 genotype, which influences the metabolism of proton pump inhibitors (PPI) including LPZ. This study examined the changes in the H. pylori eradication rates between the periods before and after the commencement of a routine genetic test for CYP2C19 at the Daiko Medical Center in Nagoya, Japan, in November, 2005. Subjects were patients who visited the Center during the period from June, 2004 to August, 2010. The patients were classified into three groups according to their CYP2C19 genotype: rapid metabolizers (RM) with a *1*1 genotype, intermediate metabolizers (IM) with a *1*2 or *1*3 genotype, and poor metabolizers (PM) with a *2*2, *2*3, or *3*3 genotype. Non-rapid metabolizers (IM and PM) were basically treated with a LAC regimen, while RMs were treated with a RAM reg imen(rabeprazole, AMPC, and metronidazole). The eradication rate was 80.0% (n=90) for the period without the genetic testing and 88.7% (n=124) for the period with the genetic testing (chi2=3.11, p=0.078). The age-sex adjusted odds ratio of eradication success was 2.29 (95% confidence interval, 0.99-5.28, p=0.051) for the latter period relative to the former period among those less than 70 years of age. Those results suggested that the routine genetic test which allows a choice of the RAM regimen for R M improved the eradication rate.