PM2.5 samples were collected for August 13–22 (non-harvest period, NHP) and for October 21–31 (harvest period, HP) in 2014 from an agricultural region of Eastern China. The samples were subsequently analysed to determine mass concentrations and fractions of elements, water-soluble ions and carbon components. Online datasets (SO2, NO2, O3, CO, PM10 and PM2.5) and meteorological conditions were synchronously monitored. The average mass concentrations of PM2.5 during the HP and NHP were respectively 108.3 and 62.6 µg m–3. Compared with the mass concentrations of organic carbon (OC), Cl–, NO3– and K+ during the NHP, those during the HP were significantly increased. Moreover, the mass fractions of OC, elemental carbon (EC), Cl– and K+ during the HP were respectively 1.6, 1.3, 3.2 and 1.3 times of those during the NHP. SO42–, NO3–, and OC were the major chemical components in PM2.5 during the HP, indicating that biomass burning and secondary transformation may be two major sources of PM2.5 during the HP. The K+/Cl– value in PM2.5 during the HP was lower than 1, indicating that maize straws were the crop residues in the study area. Although the sulphur and nitrogen oxidation ratios during the HP were lower than during the NHP, the effects of the secondary transformation on particles cannot be ignored during the HP. Biomass burning yielded a 58% OC concentration during the HP.