The aim of this study was to characterize the inorganic chemical composition of fine inhalable atmospheric particulate matter (PM2.5) in medium-sized cities in Brazil. These cities account for a significant proportion of the population and are growing at rates above the national average, thereby demonstrating the importance of carefully analysing the possible impact of such growth on air quality over the coming decades. In 2013 and 2014, this study collected PM2.5 samples from sites in the cities of Londrina and Maringa in two seasons: winter and summer. The mean concentration of PM2.5 ranged from 4.4 µg m–3 and 3.7 µg m–3 during the summer to 10.3 µg m–3 and 8.0 µg m–3 in winter in Londrina and Maringa, respectively. The analysis of the major water-soluble ions, nitrate, sulphate and chloride, showed that they accounted for between 16.5% and 35.1% from the mass of PM2.5, with sulphate providing the greatest contribution in all the campaigns. The nitrate/sulphate ratios ranged from 0.2 and 0.6, which are similar to the figures cited in the literature for other regions of the world. Although the PM2.5 concentrations are much lower than those observed in Asia and in Sao Paulo the participation of ions (%) is very close to that observed in Asian cities and significantly higher than the values recorded in other areas of Brazil, possibly as a result of the increased influence of burning of biomass and waste. The metals Zn, Pb, Cu and Mn found in the samples from all campaigns indicate that, in general, mobile sources are the main contributor to PM2.5. The winter campaigns showed the highest concentrations of black carbon equivalent (BCe). Absolute principal component analysis and enrichment factor analysis indicate the contribution of vehicular emission sources and biomass and waste burning to the inorganic chemical composition of PM2.5.