Friction Stir Surfacing(FSS)has been developed for fabrication of surface composite. The process involves rotating a solid consumable bar with one of its ends pressed hard against a substrate material such as a plate. Commercial pure aluminium and medium carbon steel is used as tool and substrate. Heat is generated at the tip of the consumable, producing a plasticized layer. Lateral movement of the substrate, relative to the rotating consumable, deposits this plasticized material on to the substrate. There is no melting of the substrate material and therefore no dilution of the substrate. The composition of the deposit is the same as that of the consumable. The deposit is inherently homogeneous and has good mechanical strength and adherence. It was also found that Fe particles fragmented in the Al matrix. The X-Ray Diffraction(XRD) resulted with ferrite and aluminum phase. A mechanism is discussed for formation of a composite surface on the steel substrate.