Background Recent studies have suggested that susceptibility to chronic obstructive pulmonary disease(COPD)might be related to the length polymorphism of(GT)_n repeat in the 5’-flanking region of heme oxygenase-1(HOX-1)gene.However,there has been no research about the relationship between the polymorphism of HOX-1 gene and severity ofCOPD.Methods The polymorphism of HOX-1 gene in 452 patients with COPD from Han population in Southwest China wasanalysed by fragment analysis.The frequencies of the HOX-1 genotype were compared with the stage of COPD of eachpatient.Results The HOX-1 genotypes were classified into two groups:group Ⅰ were individuals with class L allele(the numberof GT≥32 repeats),and group Ⅱ were those without class L allele(the number of GT<32 repeats).The genotypicfrequency of the HOX-1 group Ⅰ was significantly higher than group Ⅱ in the very severe COPD patients(36.8% vs 22.4%,P<0.01,OR=2.0,95% CI 1.3-3.1),while the genotypic frequency of the HOX-1 group Ⅱ was lower in the mild COPD(16.0% vs 26.0%,P=0.02,OR=0.5,95% CI 0.3-0.9).However,in moderate and severe stages COPD,there were similargenotypic frequencies between HOX-1 group Ⅰ and group Ⅱ.Conclusions Genetic polymorphism in HOX-1 is associated with the severity of COPD in Southwest China.COPDpatients with class L allele may be susceptible to develop very severe COPD.Conversely,the COPD patients withoutclass L allele may be more easily stabilized on mild COPD. Background Recent studies have suggested that susceptibility to chronic obstructive pulmonary disease (COPD) might be related to the length polymorphism of (GT) _n repeat in the 5’-flanking region of heme oxygenase-1 (HOX-1) gene. There, there has been no research about the relationship between the polymorphism of HOX-1 gene and severity of COPD. Methods The polymorphism of HOX-1 gene in 452 patients with COPD from Han population in Southwest China was analyzed by fragment analysis. The frequencies of the HOX-1 genotype were compared with the stage of COPD of eachpatient. Results The HOX-1 genotypes were classified into two groups: group I were individuals with class L allele (the number of GT≥32 repeats), and group II were those without class L allele ( the number of GT <32 repeats. The genotypic frequency of the HOX-1 group I was significantly higher than group II in the very severe COPD patients (36.8% vs 22.4%, P <0.01, OR = 2.0, 95% CI 1.3- 3.1), while the genotypic frequency of the HOX-1 group II w As in the mild COPD, there were similargenotypic frequencies between HOX-1 group I and group (16.0% vs 26.0%, P = 0.02, OR = 0.5, 95% CI 0.3-0.9) II.Conclusions Genetic polymorphism in HOX-1 is associated with the severity of COPD in Southwest China. COPD patients with class L allele may be susceptible to develop very severe COPD. Conversely, the COPD patients without class L allele may be more likely stabilized on mild COPD .