This study reports the stabilization of toxic heavy metals in fly ashes from incineration of municipal solid waste (MSW) in a grate furnace incinerator (GFI) and a fluidized bed incinerator (FBI) using wet milling without water-extraction pretreatment. After wet milling for 24 h, the relative leaching rates (RLRs) were decreased for all the studied heavy metals (Cr, Cu, Zn, Cd and Pb) and met the regulatory leaching concentrations as determined by Toxicity Characteristic Leaching Procedure (TCLP). For the GFI fly ash, the RLRs of Cr, Cu, Zn and Pb decreased from 11.00%, 4.27%, 5.12%, and 72.64% to 0.81%, 0.08%, 0.33%, and 1.12%, respectively. The decreased rate of RLRs for all four heavy metals had exceeded 90%. For the FBI fly ash, the RLRs of Cr, Cu, Zn, Cd and Pb decreased from 6.81%, 0.09%, 1.99%, 8.92%, and 0.10% to 1.51%, 0.05%, 1.14%, 3.05% and 0.02%, respectively. European Community Bureau of Reference (BCR) sequential extraction results demonstrate that, for the GFI fly ash, wet milling led to decreases in the water-and acid-soluble and reducible fractions, but an increase in the more stable residual fraction. For the FBI fly ash, except for Cu, the residual fraction increased while the water-and acid-soluble fraction largely decreased after wet milling.