It is well known that cigarette smoking is the major risk factor for chronic obstructive pulmonary disease (COPD). However, only 10%-20% of chronic heavy cigarette smokers develop symptomatic disease, which suggests the presence of genetic susceptibility. Microsomal epoxide hydrolase (EPHX1) is an enzyme involved in the protective mechanism against oxidative stress. It has been reported that gene polymorphisms of this enzyme may be associated with variations in EPHX1 activity. In this study, we aimed at investigating the relationship between EPHX1 polymorphisms and susceptibility to COPD in the Tunisian population. EPHX1 exon 3 (rs1051740, Tyr113His) and exon 4 (rs2234922, His139Arg) polymorphisms were genotyped by polymerase chain reaction followed by restriction fragment length polymorphism analysis. These techniques were used to examine a total of 416 Tunisian individuals, including 182 blood donors and a group of 234 COPD patients. All subjects were not related. An increased risk for COPD was observed in subjects with EPHX1 His113-His113 genotype (odds ratio = 2.168; confidence interval 1.098-4.283; p = 0.02386). However, multivariate logistic regression analysis showed no significant relationship between the mutant genotype and the disease after adjustment for sex, age, body mass index, smoking status, and pack-year smoking (odds ratio = 1.524; confidence interval, 0.991-6.058; p = 0.06137). Regarding the two subtypes of COPD, our investigations demonstrated that there is no significant correlation between exon 3 polymorphism and the chronic bronchitis subgroup (p = 0.09034). The relation between exon 3 polymorphism and emphysema was significant in the univariate analysis (p = 0.02257), but no association was found after controlling for classic risk factors (p = 0.06273). In conclusion, our results showed that there is a weak relation between 113His genotype and COPD, and no apparent relation between 139Arg and COPD in the studied Tunisian population.