Abstract: The air pollution control (APC) residues from municipal solid waste incinerator(MSWI) were classified by sizes; the heavy metals contents, speciation and their water-leaching toxicity in the size-classified fractions were analyzed; and the contribution of heavy metals content and leachable amount in various fractions to the raw APC residues was discussed. It is concluded that fractions of >154 μm and <30 μm were minor parts in the APC residues, while particles of 38.5～74 μm accounted for about 50%. Concentration of heavy metals, except Ni and Cr, were greater in fine particles, and acid soluble Cd, Zn, Pb and Cu, organically bound Pb, as well as crystalline iron oxide occluded Pb and Zn took up most of the increase. The leaching of Cr, Ni, Zn, Hg and Pb increased with decrease of particle size, especially for Zn, Hg and Pb. But the enrichment of heavy metals in fine particles was not much in evidence. The much higher heavy metals leaching ratios of fine particles made this section a bigger contributor to heavy metals leaching from raw APC residues. Especially for Pb, Zn and Hg, about 40% of their leachable sections were enriched in the fraction of <30 μm, which accounted for only about 8% of the APC residues.