The present study was undertaken to compare the hardness and transverse rupture strength (TRS) of metal-based tooling composites containing diamonds of different grit sizes. Two kinds of bond matrix, copper-based and iron-based, were applied in the fabrication of the composites. In the copper-based matrix, rare earth was used as an additive. Diamonds of three different grit sizes were incorporated into two bond matrix, thereby forming six kinds of diamond composites. SEM and EDS were used to analyze the fractured surfaces of the composites. It was found that the diamonds of medium grit size in the copper-based bond matrix led to the highest hardness and TRS. For the iron-based bond matrix, however, the hardness and TRS of the composites containing the coarsest diamonds were found to be the highest. In same bond matrix, a close relationship between TRS and hardness was established.