The influence of the aerosols particles on the lung function was investigated by the measurements of lung function parameters in children at secondary school located in the centre of city Wroclaw (south – west of Poland). Simultaneous daily indoor and outdoor measurements of PM1, PM2,5, PM10 have been conducted with the use of Harvard cascade impactors (MS&T Area Samplers). In the study 186 children age 13–14 yrs underwent repeated spirometry (Blue Spiro) at the same time of day, 5 times during the winter/spring (heating season) and 5 times in summer/autumn. Exposure to indoor fine particulate matter PM2,5 significantly worseness FEV1 in the lung function of secondary school children (Pearson correlation: median versus indoor PM2,5, r = -0,95; p < 0.05). Correlation of the lung function parameters with other particles PM1, PM10 measured indoor and outdoor were not statistically significant. PM2.5 measured outdoor was also not significantly correlated with lung function parameters. Considerable effort should be made to improve ambient air quality. Especially there is a need to measure and control the fine particulate matter PM2,5 in winter as it has the highest impact on lung function in children.