Background: Concentrations of ambient air pollution and pollutants in China have changed considerably during the last decade. However, few studies have evaluated the effects of current ambient air pollution on the health of kindergarten children.Methods: We studied 6730 Chinese children (age, 3-7 years) from 50 kindergartens in 7 cities of Northeast China in 2009. Parents or guardians completed questionnaires that asked about the children's histories of respiratory symptoms and risk factors. Three-year concentrations of particles with an aerodynamic diameter ≤10 µm (PM10), sulfur dioxide (SO2), and nitrogen dioxides (NO2) were calculated at monitoring stations in 25 study districts. A 2-stage regression approach was used in data analyses.Results: The prevalence of respiratory symptoms was higher among children living near a busy road, those living near chimneys or a factory, those having a coal-burning device, those living with smokers, and those living in a home that had been recently renovated. Among girls, PM10 was associated with persistent cough (odds ratio [OR]PM10 = 1.44; 95% CI, 1.18-1.77), persistent phlegm (ORPM10 = 1.36; 95% CI, 1.02-1.81), and wheezing (ORPM10 = 1.31; 95% CI, 1.04-1.65). NO2 concentration was associated with increased prevalence of allergic rhinitis (OR = 1.96; 95% CI, 1.27-3.02) among girls. In contrast, associations of respiratory symptoms with concentrations of PM10, SO2, and NO2 were not statistically significant among boys.Conclusions: Air pollution is particularly important in the development of respiratory morbidity among children. Girls may be more susceptible than boys to air pollution.