Municipal solid waste incinerator fly ash, comprised of a mixed cyclone ash and lime-reactant ash, can be characterized as having a high melting point; thus, it is difficult to melt effectively and economically, without modification of its components.This study investigates how modification of fly ash's basicity will affect the pozzolanic characteristics of the resultant melts. It was modified by adding SiO2, to bring the basicity closer to unity; subsequent additions of Al2O3 were also evaluated. The pozzolanic characteristics of the samples were evaluated at various curing ages. The compressive strength development, degree of hydration, hydration products, and the engineering properties of the pastes were examined. All the slag samples produced from the modified fly ash meet the ASTM C989 specifications for blast furnace slag. The results indicate that increasing the amount of aluminum oxide to raise the basicity will enhance the early hydration characteristics. XRD and DTA analyses indicated that the main hydrated products of the tested samples included calcium hydroxide (CH), calcium silicate hydrate (C-S-H), and calcium aluminate hydrates (C-A-H). The degree of hydration increased upon increasing the curing time, but decreased upon increasing the replacement ratio. The results of this study demonstrate that MSWI fly ash can be melted at a lower temperature when its basicity is modified and that it can produce the desired type of slag, having pozzolanic characteristics close to or outperforming those of ordinary Portland Cement (OPC).