Spherical particle impact damage and strength degradation phenomena of silicon nitride by several types of spheres were analysed in comparison with chipping fracture behaviour reported in the literature. It was found that steel and partially stabilized zirconia (PSZ) particles caused Hertzian cone cracks, resulting from the elastic response of the material in accordance with the Hertzian cone crack theory. In contrast, alumina and sialon particles induced both median-radial crack systems at low impact velocity range and Hertzian cone cracks at high impact velocity range. The critical impact velocity for strength deg radati on, V-c, correlated with the hardness of the spheres and target ceramics, and V-c, for Hertzian cracks and median cracks were higher than that for chipping fracture.