Carbon dioxide (CO2) laser surgery has been shown to be clinically effective in the treatment of nasal allergy. To investigate the mechanisms of eosinophil infiltration and activation underlying the therapeutic effects of CO2 laser surgery, we examined changes in the cytological profile of nasal mucosa after surgery. Twenty-two patients with perennial nasal allergy against house-dust mites underwent two or three rounds of laser surgery at 1-month intervals on an outpatient basis. The following parameters were evaluated at each visit: (i) improvement of clinical symptoms (nasal obstruction, rhinorrhea, and sneezing), (ii) percentage of infiltrating eosinophils in nasal mucosa, and (iii) the degree of EG2+ cells and intracellular adhesion molecule 1 (ICAM-1) expression by immunocytochemistry. All clinical symptoms significantly decreased after surgery. Significant reductions in eosinophil infiltration (p < 0.01) and the percentage of EG2+ cells (p < .005) were observed also. However, the degree of ICAM-1 expression in epithelial cells was not changed. These results suggest that CO2 laser surgery partially reduced the allergic reactions, leading to improvement of clinical symptoms.