The present study was undertaken to examine the effects of metal coatings on the surfaces of diamond crystals embedded in two kinds of bond matrix. Diamonds with or without coatings were incorporated into two matrices for hot-pressing, thereby forming four kinds of diamond composites. The transverse rupture strength (TRS) of the composites was measured to assess the bending strength of the composites. SEM and EDS were used to analyze the fractured surfaces of the composites. It was found that the TRS of the composites containing coated diamonds increased in both bond matrices. But the coatings in the bond matrix without rare earth increased TRS a little more than the case with rare earth due to a different failure mechanism of metal coatings.