PURPOSE: To make it possible to form a cutting tool material having a unique combination of good resistance to several failure mechanisms by dispersing single crystals having specific sizes and shapes as reinforcing materials into a preform of silicon nitride or alumina.

CONSTITUTION: This cutting tool material has the compsn. formed by homogeneously dispersing the single crystalline materials, such as whiskers, at max. 35 wt.% with the preform of the silicon nitride or alumina and is improved in the toughness behavior in a wide range of metal cutting applications. The single crystalline materials, such as whiskers, are classified to three kinds of the following types; (i) to (iii) having characteristics in the shapes and sizes. (i) the single crystalline fibers having a diameter smaller than 1 μm and an aspect ratio of 15 to 150; (ii) single crystalline fibers having a diameter of 1 to 6 μm and an aspect ratio of 5 to 100 and (iii) single crystalline disks having the corresponding diameter of 5 to 50 μm and an aspect ratio of 5 to 50. At least two kinds among three kinds of these single crystals (i to iii) are compounded at least at 5 wt.% with the preform.