© (2007) Trans Tech Publications, Switzerland.Diamond segments were fabricated by cold pressing and sintering under pressure at the temperature up to 750 °C. It was obtained from this study that if we increase the cobalt ratio, the hardness of the matrix increases and the wear rate of the segments decreases. But the optimum matrix composition with less wear rate must ensures that the acceptable matrix toughness. Because the harder matrix wears more slowly than the diamonds, the space between the cutting edges and the matrix is constantly reduced. Because the swarf cannot be carried away properly, and the segment will continuously lose its ability to cut. From this point of view, the cobalt ratio in matrix composition for this formulation should not be higher than the 60 wt.% in order to have a good cutting ability.