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Vitrification was used to convert hazardous metal-bearing fly ash from municipal solid waste (MSW) incineration into useful products in this work. In addition to volume/mass reduction, some parameters such as basicity, metal leachability, density, porosity, water absorption, and compressive strength of the slags and ingots vitrified from fly ash and fly ash/additive (bottom ash and cullet) mixtures (at 1450°C for 1.5 h) were investigated. The more the bottom ash or cullet added to the fly ash, the lower the specimen basicity, leading to a more amorphous glassy matrix. Amorphous glassy slags were obtained when the specimen basicity was around 0.24-1.24. All slags were in compliance with the limits of TCLP (Toxicity Characteristic Leaching Procedure) in Taiwan, United States, and Japan. The vitrification process reduced the leaching amount and ratio of Cr and Pb, significantly lowered the leaching ratio of Cd, but raised the leaching ratios of Zn and Cu. The slag metal leachability (particularly for Cu) was mainly influenced by the metal content in slags, not the slag (crystal or glassy) structure or basicity. After vitrification, an over 50% specimen volume reduction was achieved and most of the specimen mass moved to the slag phase. The ingots, mainly consisting of Fe, also met Taiwan and U.S. TCLP requirements and were suitable for a higher purity metal recovery. The slags and ingots were approximately 2- and 6-fold as dense as the specimens before vitrification, respectively. The slags were found to have very small porosities, low water absorptions, and high compressive strengths (>550 kg/cm 2 ), so they may be considered as candidate materials for waterproof and construction.