BACKGROUND: Impulse Oscillometry is a noninvasive and effort-independent test used to characterize the mechanical impedance of the respiratory system. The clinical potential of the 105 is rapid and demands only passive cooperation which makes it especially appealing for children, for epidemiologic surveys and for conditions in which quiet breathig instead of forced expiratory maneuvers are preferred. However, several studies have shown conflicting results that the role of 108 about detection of smoking induced small airway diseases or early airway obstruction METHODS: Study was to evaluate the clinical ability of the 108 to detect about smoking induced early airway obstruction in persons with normal spirometry test. Respiratory asymptomatic study groups were formed that one is non-smoking group, another is smoking group. RESULTS: The parameters of spirometry were not significantly differences between non-smoking group and smoking group. Among the parameters of 108, total resistance(non-smoking group: smoking group= 2.22 +/-1.20 : 2.58 +/-1.71), peripheral resistance( 1.25 +/-0.62 : 1.47 +/-0.10), bronchial compliance(0.44 +/-0.12: 0.47 +/-0.16) were not statistically significant different (p<0.05), but central resistance and lung compliance were not statistically significant different (unit ; resistance= hPa/l/s, compliance= 1/hPa). Resistance(Rrs) was not statistically significant different with changes of frequences(5, 10, 15, 20, 25, 30, 35Hz), but Reactance(Xrs) was statistically significant differenct with low frequences that X5(non-smoking group : smoking group= -0.62 +/-0.28 : - 0.76 +/-0.48, p<0.001) and X10(-0.06 +/-0.19 : -0.15 +/-0.33, p<0.013) (unit; hPa/l/s, hPa=cmH2O) CONCLUSION: Impulse oscillometer(IOS) is clinically available method to detect about smoking induced early airway obstruction. And clinically potential parameters of IOS were considers that total resistance, peripheral resistance, bronchial resistance, and reactance of low frequency at 5Hz, 10Hz.