It has been reported that the particulate matter under 10 µm (PM10) has deleterious effects on respiratory health. The purpose of this study was to assess the influence of PM10 upon normal children's lung function. The subjects were 368 middle school students in two areas of Incheon Metropolitan City. One (Incheon) is in the central city and the other (Ganghwa) is in the suburbs. Air pollution data in the vicinities of two participating schools were obtained from monthly report of air quality from Korean Ministry of Environment in 2000. Pulmonary function testing (PFT) was done two times, the first one in March and the second one in December with the same students. We analyzed the relationship between the PM10 levels and pulmonary functions (FEV1, FVC) of the children. The monthly average of the PM10 level between the two areas showed no significant difference (55.3 vs. 52.3 µg/m3). In both regions, the difference of the PM10 level between March and December was statistically significant (64 vs. 56 µg/m3 in Incheon, 64 vs. 54 µg/m3 in Ganghwa). The findings of the PFT values in March were significantly lower than those values found in December for both regions. In conclusion, we suggest that PM10 has some adverse effect on the pulmonary function of normal children.