Municipal solid waste incinerator (MSWI) fly ash was vitrified at ∼1450°C, for the first time, using Brown's gas. Vitrification of pelletized fly ash (fly ash + water glass) results in a decrease of the leaching of toxic heavy metals to much below the Korean regulatory limit values, although melted fly ash was a poorly vitrified product that had a dark gray appearance. The addition of glass cullet to the fly ash increased the silica content and decreased the basicity. It was determined that a decrease in basicity from 2.94 to 0.28 leads to good vitrified products that have an amorphous glassy structure that is dark brown in color. Leaching all of the potentially hazardous heavy metals present in fly ash also decreased as the basicity decreased. It was determined that all the heavy metals (zinc, lead, chromium, arsenic, copper, manganese, and cadmium) were efficient in regard to substituting for parent Al and Ca ions in the silicate structure. It was further confirmed by scanning electron microscopy and X-ray diffractometry studies that the initial crystalline structure of fly ash was transformed to an amorphous glassy structure upon vitrification. The vitrified products of fly ash and its mixtures with glass cullet were determined to be nonhazardous in nature and glassy in appearance; therefore, they could be considered as construction and road-building materials in the future.