Abstract: The basic properties of three fly ash samples taken from three different municipal solid waste (MSW) incinerators in China were explored by a serious of experiments, concerning their chemical composition, weight loss during calcination, melting point and leaching toxicity etc. The effect of chemical composition of fly ash on its chemical and physical characteristics as well as leaching toxicity was mainly investigated. It was found that physical and chemical characteristics of fly ash are mainly affected by the mass percentage of MgO, CaO, SiO2 and CaCl2. Fly ash with higher MgO and Al2O3 content and lower CaCl2 content has relatively higher melting point. Fly ash with higher CaO and CaCl2 content has relatively higher moisture and weight loss in calcination. Fly ash with higher SiO2 content has lower leaching rate of heavy metal.