Fly ash from municipal solid wastes (MSW) incinerators in Korea contains a large amount of toxic materials and requires pertinent treatments. However, since fly ash in Korea has a high chlorine concentration, it is difficult to apply cementation and chemical treatment techniques. In this study, we report the vitrification of fly ash along with the properties of the glasses and leaching characteristics of heavy metal ions. Fly ash can be vitrified by melting at 1500 degreesC for 30 min with the addition of >5 wt.% of SiO2. Glasses showed Vickers hardness of 4000-5000 MPa, bending strength of 60-90 MPa and indentation fracture toughness of similar to0.9 MPa m(1/2). Glasses also showed the excellent resistance against leaching of heavy metal ions with Cd2+ < 0.04 ppm, Cr3+ < 0.02 ppm, Cu2+ < 0.04 ppm and Pb2+ < 0.2 ppm. These results indicate that the vitrification technique is effective for the stabilization and recycling of toxic incinerator fly ash. (C) 2002 Elsevier Science B.V All rights reserved.