Bronchial asthma (BA) and chronic obstructive pulmonary disease (COPD) are two inflammatory diseases characterized by airflow obstruction.Both diseases have different pathogenic mechanisms.CYP2R1 is enzyme to metabolize vitamin D.In this study, we examined the CYP2R1 gene polymorphisms (rs10741657) in a Japanese adult population.Methods:DNA specimens were obtained from the following three groups:47 patients with bronchial asthma(BA), 48 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 AA/AG genotype of rs10741657 were higher than that of the GG genotype in COPD patients compared to BA patients and controls (P<0.001 and P<0.001, respectively ).Comparison of the clinical characteristics in both patients according to the CYP2R1 gene polymorphisms (rs10741657) showed that the count of peripheral blood eosinophils  in AA/AG genotype in COPD patients were lower than that in both (AA/AG, GG) genotype in BA patients  (P<0.05 and P<0.05, respectively ).And FEV1 in AA/AG genotype in COPD patients was also lower than that  in both (AA/AG, GG) genotype in BA patients  (P<0.05 and P<0.05, respectively ).Conclusions:We were the first to show that CYP2R1 gene polymorphism (rs10741657) in Japanese patients with COPD is different from that with BA.