Background: We tried to examine the small airway diseases which can be found early, in workers exposed to inorganic dusts. This is measured in normal breath by using the impulse oscillometry (IOS). Methods: The Pulmonary function test (forced vital capacit [FVC], forced expiratory volume in one second [$FEV_1$], forced expiratory flow between 25% and 75% of vital capacity [$FEF_{25-75}$]), IOS resistance (Rrs at 5, 10, 15, 20, 25, 35 Hz) and reactance (Xrs at 5, 10, 15, 20, 25, 35 Hz) were measured for 454 workers. The subjects were classified into 173 workers of normal (38.1%) and 281 patients with pneumoconiosis (61.9%). Results: There were significant differences between normal and patients with FVC ($3.82{pm}0.61$ vs. $3.53{pm}0.56L$), $FEV_1$ ($2.67{pm}0.63$ vs. $2.35{pm}0.48L$), and $FEF_{25-75}$ ($1.88{pm}0.95$ vs. $1.47{pm}0.80L/sec$) between groups (p<0.05). And as for IOS, there was no significant difference in resistance (Rrs) (p>0.05), and there were significant differences between normal and patients with reactance (Xrs) 15 Hz ($0.003{pm}0.05$ vs. $-0.006{pm}0.04kPa/L/s$), 20 Hz ($0.043{pm}0.05$ vs. $0.031{pm}0.04kPa/L/s$), and 35 Hz ($0.141{pm}0.05$ vs. $0.131{pm}0.05kPa/L/s$) between groups (p<0.05). Conclusion: We could find out that 15 Hz, 20 Hz, and 35 Hz values of reactance were significantly influenced by pneumoconiosis. When usefulness and reproducibility to carry out the IOS are considered, it is thought that in future work will be required to draw the reference values for normal Korean persons.