Thick metal/diamond composite coatings on Al substrate were deposited by cold spray process with in-situ powder preheating.  Microstructural characterization of the as-sprayed coatings with different diamond size, strength and with/without Ti coating was carried out by OM and SEM.  Assessment of basic properties such as tensile bond strength, porosity, and hardness of the coatings and the deposition efficiency was also carried out.  Particular attention on the coatings was the diamond fracture phenomenon during deposition and the interface between diamond and metal matrix.  The potentials and the problems of metal/diamond composite coatings by cold spray are discussed.