To obtain a diamond sintered compact having superior chipping and heat resistances at a low cost by mixing diamond powder with powder prepd. by partially carbonizing a resin and a phosphorus compd. and sintering the resultant mixture under conditions of specified pressure and temp.

Diamond powder is mixed with powder of a nondiamond carbonaceous material prepd. by partially carbonizing a resin and a phosphorus compd. and the resultant mixture is sintered by holding under conditions of ≥3GPa pressure and ≥1,000°C temp. to obtain the objective sintered compact. The phosphorus compd. is used as a sintering aid and phosphate or hydrogenphosphate of a group III element of the Periodic Table, its hydrate or a mixture of oxide of a group III element of the Periodic Table with phosphorus oxide or phosphate of the element is especially used. The diamond powder as starting material is, e.g. synthetic, natural or polycrystalline diamond powder.