To investigate the pollution characteristics of water-soluble ions in aerosols in the urban area of Beibei District, Chongqing, graded aerosol samples were continuously collected by a cascade impactor (Andersen) from March 2014 till February 2015. Water-soluble ions, namely, Na+, NH4+, K+, Mg2+, Ca2+, F–, Cl–, NO3– and SO42– in different particle-size ranges (< 0.43, 0.43–0.65, 0.65–1.10, 1.10–2.10, 2.10–3.30, 3.30–4.70, 4.70–5.80, 5.80–9.00 and 9.00–100 µm), were measured by ion chromatography. The results showed that Mg2+, Ca2+ and F– mainly appeared in coarse particles, and other ions were mainly distributed in fine particles. SO42– was mainly distributed in the droplet mode in spring and autumn from in-cloud processes, while SO42– had both condensation and droplet modes in summer from the oxidation of SO2. NH4+ and SO42– were mainly present in the form of NH4HSO4 in aerosols. Except during summer, NO3– mostly existed in the forms of NH4NO3 in fine particles and Ca(NO3)2 in coarse particles. Na+ was single-peaked in spring and summer and double-peaked in autumn and winter. Fine-mode K+ showed a single-peak distribution in every season. The existent forms of Cl– were KCl in the fine mode and CaCl2 in the coarse mode. Mg2+ was mainly distributed in coarse particles, which showed a bimodal pattern distribution in spring and summer. Ca2+ mainly existed in coarse modes, whose concentrations increased with particle size. The emissions from motor vehicle exhaust, combustion processes, soil and construction dust were the major sources of water-soluble ions in this area. SOR (the sulfur oxidation ratio) was the highest in summer and the lowest in winter, but NOR (the nitrogen oxidation ratio) was highest in winter. The SOR values for condensation-mode (0.43–0.65 µm) exceeded 0.10 only in summer. SOR was considerably higher than NOR for the same particle sizes during the whole year.