RATIONALE: Epidemiological evidence indicates ambient exposure to PM2.5 have 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 pre- to early adolescent schoolchildren. OBJECTIVES: To examine long-term effects of PM2.5 within the 4-yr average concentration range of 10 to 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 to 12 from 16 school communities in 10 cities around Japan, covering a board area of the country to represent concentration range of PM2.5, was done with multilevel linear regression model. Forced expiratory volume in 1 second (FEV1), forced vital capacity (FVC), and aximal expiratory flow at 50% of FVC (V50) were used as lung function indicators to examine effects of 10-μg/m3 increases in PM2.5 concentration on relative growth per 10-cm increase in height. MEASUREMENTS AND MAIN RESULTS: Overall annual mean PM2.5 concentration was 13.5 μg/m3 (range: 10.4 to 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 ;pre-adolescent boys and pre- to early adolescent girls.