To investigate the pollution characteristics and sources of watersoluble inorganic ions（WSIIs） in particulate matter with different particle sizes during winter，ultrafine particle（PM₁），fine particulate matter（PM_2.5），and inhalable particles（PM₁₀） samples were collected in Hohhot from January 5 to February 4，2017. Eight kinds of WSIIs were determined using ion chromatography（IC）. Their compositions，existing forms，and secondary transformation characteristics were analyzed. The results suggested that the average daily WSIIs concentrations ofPM₁，PM_2.5， and PM₁₀ on polluted days were 3.1，3.1，and 3.0 times that observed on clean days，accounting for 37.1%，40.5%，and 29.9% of the total mass concentration of particulate matter，respectively. Sulfate（SO₄^2-），nitrate（NO₃^-），and ammonium（NH₄⁺）［abbreviated as SNA］ were the predominant ions of WSIIs on polluted days，accounting for 73.3%，75.0%，and 74.0% of the total WSIIs in the three kinds of particulate matter，respectively. The concentrations of chloride ion（Cl^-） inPM₁，PM_2.5， and PM₁₀ on New Year's Eve were 8.0，7.3，and 6.5 times that observed on clean days，respectively. The concentrations of magnesium ion（Mg²⁺） on New Year's Eve were 11.2，8.3，and 5.6 times that observed on clean days，respectively. This indicated that fireworks had a greater contribution to the Cl^- and Mg²⁺ in particulate matter in Hohhot. The ratio of anion to cation equivalent concentration（AE/CE） inPM₁ and PM_2.5 was >1，whereas that in PM₁₀ was <1，highlighting noticeable differences in aerosol acidity. The AE/CE of the three kinds of particulate matter on New Year's Eve were 2.3，1.8，and 1.6，respectively. The result indicated that the three kinds of particulate matter were strongly acidic，which was mainly related to the large number of anions emitted by fireworks. During polluted days，SNA predominantly existed as ammonium sulfate［（NH₄）₂SO₄］，Ammonium bisulfate（NH₄HSO₄），and ammonium nitrate（NH₄NO₂），while on New Year's Eve，SNA existed as NH₄HSO₄ and NH₄NO₂. The results of secondary transformation showed that sulfate and nitrate were not only derived from primary emission，but also from the secondary formation of the heterogeneous aqueous reaction of gaseous precursors.