Daily PM2.5 samples were collected at a rural background station (JinYun) located in Chongqing across four consecutive seasons from October 2014 to July 2015. Major water-soluble inorganic ions (WSII), organic carbon (OC) and elemental carbon (EC) were analyzed, and their chemical characteristics, transport pathways and potential source regions were investigated. The annual average of PM2.5 concentrations was 56.2 ± 31.0 μg m-3, of which secondary inorganic aerosol (SNA) and carbonaceous aerosols accounted for 41.0% and 29.4%, respectively. Higher concentrations and contributions of SO42- were observed in summer than autumn and spring, likely caused by the secondary transformation of SO2 to SO42-. In addition, transportation from the urban area of Chongqing (Yubei) also played an important role for the elevated SO42- levles in summer. Aqueous-phase reactions played important roles for the accumulation of PM2.5 during pollution period in winter. However, on an annual basis homogeneous gas-phase reaction might dominate the NO3- formation. Aerosol environment was ammonium-rich and NH4+ formation promoted the production of NO3- under lower temperature. Carbonaceous content, of which 81.0%–84.6% was organic carbon, was higher in winter than that in other seasons. Primary organic carbon (POC) represented 50.0%–77.2% of the total OC. Analysis using potential source contribution function (PSCF) suggests the site was mainly affected by regional pollutant sources, e.g., the southwestern and northern areas of Chongqing.