OBJECTIVE To study the expression of a specific inhibitor of endogenous carbon monoxide (CO) generating enzyme Heme oxygenase-1 (HO-1) in allergic rhinitis guinea pigs. METHODS Guinea pigs were divided into three groups,one were sensitized by using ovalbumin intraperitoneal and nasal challenge, the second group were treated with dexamethasone as therapy group, the third group were treated with saline for control. The infiltration of eosinophil (EOS) with HE staining and the expression of HO-1 by immunohistochemical staining were observed in nasal mucosa. RESULTS Most of infiltrating cell in mucosa were EOS and the amount of infiltrated EOS related to the level of inflammation,and HO-1 was found mainly located in cell plasma off glandular epithelium of mucosa. The sensitized groups showed that the highest optical densities of HO-1 (P <0. 01) and the most EOS (P < 0.01) were in epithelium, and the therapy group showed lower optical densities of HO-1 (P <0.01) and few of EOS (P <0.01) than sensitized group, but higher than the control group. There was a significant difference between the three groups (P <0.01). CONCLUSIONS HO-1 is mainly located in cell plasma of glandular epithelium of nasal mucosa, and the degrees of expression of HO-1 positive correlate with the process of inflammation in allergic rhinitis guinea pigs, which suggests that the endogenous carbon monoxide might play a significant role in the pathogenesis of allergic rhinitis.