In the last few years, there has been lot of research works all over the world dealing with the management of municipal solid waste (MSW) and its impact on environment and sustainability. In Lebanon this problem has caused uprising in the country leading to a major influence on the Lebanese society. The review of MSW management scheme has indicated that the amount of MSW sent to incineration plants will increase in Lebanon. Therefore, the amount of incinerated MSW residues generated will also increase accordingly in the coming years. This paper presents a study of the Physical and Chemical characterization of the municipal solid waste incinerated fly ash (MSWI) in Lebanon which includes, fineness, mineral components, oxides, heavy metals content. The objective of this study is to investigate the feasibility of the using these ashes in concrete. It was found that more that 87% of the fly ash particles have diameters smaller than 0.045 mm. The fly ash particles tend to be alkaline (pH ≥12); the loss on ignition at 1050 C is 12. The main elements are Ca, Na, Cl, Si, K, Na, Al, O and S, and the main compounds are (in order of amount: CaO, SiO2, Al2O3. Heavy metal elements are Zn, Pb, Cr, and Cu. It was found that the content of heavy metals is very low and not exceeding the hazardous wastes limits. Thus, the potential use of this type of MSWI fly ash is of great importance to be considered as partial cement replacement in construction applications. Keywords: Municipal Solid Waste, Incineration, Fly Ash, Waste Management