BACKGROUND: The effects of exercise on pulmonary function are complex and have been the subject of many investigations. But, there has been disputes about the effect of exercise on spirometric parameters and there is no study about the effect of exercise on IOS(Impulse Oscillometry)parameters. lOS, a new method of pulmonary funtion test, is based on the relationship between the pressure and flow oscillation which is produced by applying sinusoidal pressure oscillation to the respiratory system via the mouth. METHOD: Fifty-nine young adults without respiratory symptoms were divided into three groups according to degree of exercise(hard exercise group: mean exercise time is over three hours per week at least for the last one month, light exercise group: between thirty minutes to three hours, nonexercise group : less than thirty minutes) and undertaken pulmonary function test(simple spirometry and IOS). RESULTS: The effects of exercise on spirometric parameters ; percentage of predictive value of forced vital capacity(FVC % pred) was higher in hard exercise group than nonexercise group(hard exercise group:102.4+/-14.8, nonexercise group: 93.7+/-9.9, p= 0.017), but there was no significant diffetence in percentage of predicted value of forced expiratory volume in one second(FEV 1% prod) and percentage of predicted value of forced expiratory flow 50% (FEF 50% pred) between groups. The effects of exercise on LOS parameters : Reactance at 5Hz(X5) was significantly lower in hard exercise group than nonexercise group(hard exercise group: -0.166+/-0.123hPa/1/s, nonexercise group: 0.093+/-0.036hPa/1/s, p= 0.006) but there was no significant difference in central resistance(Rc), peripheral resistance(Rp), resonance frequency(RF) and resistance at 5Hz, 20Hz between groups. CONCLUSION: Hard exercise increased FVC % pred on spirometric parameters and decreased reactance at 5Hz (X5) on lOS parameters.