The relationship between critical impact velocities (V_c) on crack initiation and materials properties for silicon nitride having different microstructure was investigated. All silicon nitride ceramics showed Hertzian cone crack at impact over V_c^H and it showed clear relationship with K_IC according to Hertzian cone crack theory, however, the relationship between Young's modulus was not defined clearly. Relative to V_c^R for ring crack initiation does not show exact relationship between bending strength and Young's modulus. In the silicon nitride having higher K_IC, of which included 30-50μm needlelike grains, Hertzian cone crack growth was suppressed from surface ring crack and Hertzian cone crack extension were also suppressed.