To investigate the pollution characteristics of water soluble ions in PM2.5 and PM₁₀ under severe haze days, both PM2.5 and PM₁₀samples were collected in a city of northeast China under severe haze days during October 20-2,3. Nine water-soluble ions in PM2.5 and PM₁₀including F-, Cl-, NO₃-, SO₄2-, Na+, NH₄+, K+, Mg2+and Ca2+ were analyzed. The results showed that the concentrations of all water-soluble ions mass concentration in night were higher than those in day time, with a ratio of 1.68 for PM2.5in haze days. The concentrations of SO₄2-, NO₃-and NH₄+were higher and their percentage in PM2.5 were 11.03％,8.3％ and 7.39％ in haze days, the same results in PM₁₀ were obtained. The percentages of K+and Ca2+in haze and non-haze periods were similar. Based on the ratio of different ions, the pollution from stationary sources were higher than that from mobile sources in haze days, this showed that meteorological factors had greater influences. In comparison with the data of water soluble ions during October and November of 2009, the concentrations from mobile sources were on the rise.