Micro sized particles such as SiC, Al2O3 and diamond particles reinforced with metal matrix composites are most commonly used in high performance applications like military, automotive and aerospace industries. Nowadays nano sized particles are replacing the micro sized particles because of their improved physical and mechanical properties. This paper reviews the stir processing method, mechanical properties, effect of particle size on properties of composites and structure of the metal matrix composites reinforced with nanoparticles. Among the variety of liquid metallurgy techniques processes available for preparing metal matrix composites, stir casting technique is generally accepted route and currently practised commercially because of its simplicity flexibility and Uniform distribution. © (2014) Trans Tech Publications, Switzerland.