In this investigation, LM-25 AI/SiCp as cast metal matrix composites materials joined by diffusion bonding process. Diffusion bonding is a solid state joining process which is being used extensively in recent times due to its advantages such as low heat input, production efficiency, ease of manufacture and environment friendliness. Materials that are difficult to weld by fusion welding processes can be successfully welded by diffusion bonding. In this investigation, an attempt was made to optimize the process parameter for effective joining of LM-25 AI/SiCp as cast metal matrix composites materials. The process parameters such as time, temperature and pressure have greater influence on strength of the joints. Optimization of process parameters is the key step in the Taguchi methods to achieve high quality without cost inflation. Optimization of multiple response characteristics is more complex compared to optimization of single performance characteristics. The multi-response optimization of the process parameters viz., UTS, hardness on Diffusion Bonding (DB) of LM-25 AI/SiCp as cast metal matrix composites using orthogonal array (OA) with Grey relational analysis is reported. The maximum ultimate tensile strength could be obtained for the joint fabricated under the bonding condition of temperature of 600oC, pressure of 200 MPa and, time of 25 min. Keywords : Optimization, Grey relational analysis, DB, Aluminium - metal matrix composite