Rationale: Epidemiological evidence indicates that ambient exposure to particulate matter <2.5 μm in aerodynamic diameter (PM2.5) has adverse effects on lung function growth in children, but it is not actually clear whether exposure to low-level PM2.5 results in long-term decrements in lung function growth in preto early-adolescent schoolchildren. Objectives: To examine long-term effects of PM2.5 within the 4-year average concentration range of 10-19 μg/m3 on lung function growth with repeated measurements of lung function tests. Methods: Longitudinal analysis of 6,233 lung function measurements in 1,466 participants aged 8-12 years from 16 school communities in 10 cities around Japan, covering a broad area of the country to represent concentration ranges of PM2.5, was done with a multilevel linear regression model. Forced expiratory volume in 1 second, forced vital capacity (FVC), and maximal expiratory flow at 50% of FVC were used as lung function indicators to examine the effects of 10-μg/m3 increases in the PM2.5 concentration on relative growth per each 10-cm increase in height. Results: The overall annual mean PM2.5 level was 13.5 μg/m3 (range, 10.4-19.0 μg/m3). We found no association between any of the lung function growth indicators and increases in PM2.5 levels in children of either sex, even after controlling for potential confounders. Analysis with two-pollutant models with O3 or NO2 did not change the null results. Conclusions: This nationwide longitudinal study suggests that concurrent, long-term exposure to PM2.5 at concentrations ranging from 10.4 to 19.0 μg/m3 has little effect on lung function growth in preadolescent boys or pre- to early-adolescent girls.