The atmospheric PM_2.5 samples are collected day and night in Nanjing,Changzhou and Suzhou from 16 November to 17 December 2010,the concentrations of water-soluble ions and elements are analyzed,and the characteristics of PM_2.5 and inorganic elements are discussed.Results show that the daily mean values of PM_2.5 in Nanjing,Suzhou and Changzhou are more than the national air quality criteria(75 μg/m³).The pollution of PM_2.5 in Suzhou is the most serious,Changzhou the less,and Nanjing the least.SO₄^2-,NO₃^-,Ca²⁺ and Mg²⁺ are the major inorganic ions in PM_2.5 in the three cities.The correlation analysis shows that there is a significant correlation between Na⁺and Cl^-in Suzhou,which is influenced by sea salt transportation.Ca and Al are the major elements in PM_2.5 in the three cities.The principal component analysis shows that PM_2.5 in the three cities is influenced by many pollution sources,which include biomass burning,surface dust,five metals factory and automotive exhaust emission.