Bronchial asthma (BA) and chronic obstructive pulmonary disease (COPD) are identified  as an airflow obstruction caused by bronchial inflammation, but both diseases have different pathogenic mechanisms.CYP2R1 is known as enzyme to metabolize vitamin D.Some articles reported that single nucleotide polymorphisms (SNPs) of this enzyme relate to BA and COPD.In this study, we examined the CYP2R1 gene polymorphisms (rs12794714) in a Japanese adult population.Methods:DNA specimens were obtained from the following three groups:45 patients with bronchial asthma(BA), 45 patients with COPD, and 50 normal controls.Allelic discrimination assay for single nucleotide polymorphisms(SNPs) relating to the CYP2R1 gene expression was carried out by using previously described SNPs detective system, sequence-specific thermal-elution chromatography.And we measured the count of peripheral blood eosinophils, neutrophils and serum IgE.Spirometry was performed with measurement of forced expiratory volume in 1 s (FEV1) and the forced vital capacity (FVC).Results:The frequencies of the GG genotype of rs12794714 were lower than that of the AA/AGG genotype in COPD patients compared to BA patients (P<0.05).Comparison of the clinical characteristics in COPD patients according to the CYP2R1 gene polymorphisms (rs12794714) showed that the count of peripheral blood eosinophils were higher in GG genotype compared to AA/AG genotype (P<0.05).FEV1 tended to be lower in GG genotype compared to AA/AG genotype in COPD patients, but there were no significant differences.Conclusions:CYP2R1 gene polymorphism(rs12794714) in Japanese patients with COPD was different from that with BA. It may relate to peripheral blood eosinophils.