PURPOSE: To produce a titled composite sintered structural body having excellent hardness, mechanical strength and toughness by mixing cubic BN powder, cermet powder consisting of ceramics and metal and Al powder at a specific ratio and sintering the mixture under adequate conditions.

CONSTITUTION: A powder mixture consisting of 40W80wt% cubic BN particle powder, 52W10% cermet particle powder which is a sintered alloy consisting of ceramics of carbide, boride, nitride, silicide, etc. and metal of ≥1 kind among Ni, Co, Cr and Si and 8W10% Al particle powder is used as a raw material for sintering. Such powder mixture is subjected to hot press sintering under the conditions of 1,100W1,250°C sintering temp. and 20,000W30,000kg/cm2 sintering pressure. Then the Al powder melts to fill the gaps among the particles and at the same time the cubic BN particles and the metallic parts of the cermet particles are subjected to liquid phase sintering. The composite sintered structural body consisting of the cubic BN and cermet is thus obtd. at a low cost.