A preform for a composite material which has high strength and excellent air permeability and hence is applicable to a high-speed die casting method and which is capable of forming a metal composite material having excellent mechanical properties by a high-speed die casting method. Also provided is a process for producing such a preform. Ceramic fibers or/and ceramic particles are mixed with a silica sol and calcium carbonate and sintered at a predetermined temperature to form a calcium/silicon sinter obtained from the silica sol and calcium carbonate. The calcium/silicon sinter coats the ceramic fibers or/and ceramic particles so that a preform having the fibers or/and the particles bound to each other by the calcium/silicon sinter is obtained. The preform for a composite material has high strength and excellent air permeability and is applicable to the high-speed die casting method capable of attaining high productivity.