In the present study, a novel procedure was introduced for casting of metal matrix composites by adding a mortar consisting expandable polystyrene beads, carboxy methyl cellulose paste, SiC particles and water as a mould pattern. This process was applied for A356 Aluminium alloy/SiCP composite. Technology of this method is based on a balance between the solidification rate and the buoyancy of the reinforcement particles. The experimental results show that effective parameters in fabrication of a sound part are density and size of pre-puff polystyrene beads, percentage of the reinforcement particles, mould material, thickness of mould cavity, casting temperature and cooling rate. However, the innovative method will only be successful for the thin-wall parts, which their solidification times become shorter than the floatation time of the reinforcement particles.