Carbonaceous fiber has high strength, high modulus and high thermal conductivity. Preforms were fabricated by suction filtration method. Regardless of fiber type, the buckling strength and elastic modulus of preforms increased with quantity of aluminum borate (AlBO) whisker addition. The carbon nano tube (CNT) preforms were not buckled but only elastically compressed. Carbonaceous fiber reinforced Al, Mg composites were fabricated by squeeze casting. CF+AlBO hybrid reinforced composites were fabricated with 5% or less deformation. On the other hand, 60% deformation was found in CNT+50AlBO hybrid reinforced composites.