Abstract: Fly ash samples from a hazardous waste incinerator burning 70 % industrial wastes and 30 % medical wastes were analyzed for heavy metals. The leaching toxicity, chemical form and concentration distribution of heavy metals were examined. The results suggested that Cd, Pb and Zn were the main heavy metals and the contents of those metals were as several times as those in fly ash from an MSW (municipal solid waste) incinerator. Heavy metals existed as exchangeable, bound to carbonates, metal oxides, organic matters and residual forms. In all heavy metals, Cd, Pb and Zn showed the higher leachability while As, Cr and Cu were more chemically steady. Cd and Cu mainly concentrated on small particles. Pb and Zn were enriched on 50-125μm and 125-250μm particles.