Objective To examine the levels of nitrite /nitrate( NO2 /NO3 ) , IL-4 and IFN-γin exhaled breath condensates( EBCs) in patients with asthma, and to investigate the effect of corticosteroid treatment. Methods Forty patients diagnosed as mild to moderate asthma were recruited. Among them, twenty were newly diagnosed and steroid naive( non-treatment group) . The other 20 patients had been treated with corticosteroid treatment( treatment group) . Twenty healthy volunteers were enrolled as normal control.EBC samples were taken for measurement of NO2 /NO3, IL-4 and IFN-γlevels. Serum IL-4 and IFN-γ concentrations were also measured. Results NO2 /NO3 level in EBC of the non-treatment group was significantly higher than that of the normal controls and the treatment group[ ( 48. 55 ±27. 37) μmol / L vs( 24. 51 ±18. 22) μmol /L, ( 36. 06 ±25. 13) μmol /L, respectively, both P lt; 0. 05] , and no significant difference was found between the treatment group and the normal controls( P gt;0. 05) . The IL-4 and IFN-γ levels in both EBC and serum had no significant difference between the three groups ( all P gt; 0. 05) . Conclusion NO2 /NO3 in EBCs increases in asthmatic patients, and decreases after corticosteroid treatment. Whether IL-4 and IFN-γlevels can be used for reflecting airway inflammation need further study.