To produce the diamond sintered compact which is used for a drilling bit and has high strength and also is excellent in fracture resistance, heat resistance, acid resistance and wear resistance, under industrially-producible conditions and at a low cost by using an oxide or double oxide of an iron group metal(s) as a sintering aid for the sintered compact.

This sintered compact comprises 1 to 20 vol.% of a material consisting of a compound that contains an iron group metal(s) and oxygen, and the remainder of a diamond powder having a 20 to 200 μm average particle size. As the compound contg. an iron group metal(s) and oxygen, an oxide of an iron group metal or a double oxide or solid solution of iron group metals, such as FeO, CoO or CoFe2O4, is used. This production of the diamond sintered compact for a drilling bit comprises: mixing a powdery oxide or double oxide of an iron group metal(s) with a diamond powder having a 20 to 200μm average particle size or a powdery mixture of this diamond powder and non-diamond carbon to obtain a mixed powder; and maintaining the resulting mixed powder under pressure and temp. conditions within the thermodynamically stable region of diamond to sinter the mixed powder.