The effect of α/β phase on the mechanical properties and contact damage of silicon nitrides Si3N4) was investigated. Silicon nitride materials were prepared from two starting powders, at selective increasing hot-pressing temperatures to coarsen the microstructures: (i) from relatively coarse α-phase powder, essentially equiaxed α-Si3N4 grains, with limited, slow transformation to β-Si3N4 grain; (ii) from relatively fine α-phase powder, a more rapid transformation to β-Si3N4, with attendant grain elongation. The resulting micro-structure thereby provided a spectrum of α/β phase ratios, grain sizes, and grain shapes. Fracture strength, hardness, and toughness were measured, and contact damage and strength degradation after indentation were investigated by Hertzian indentation using spherical indenter. A brittle to ductile transition in Si3N4 depended on α/β phase ratio as well as grain size. Silicon nitride with elongated β grains showed a superior, contact damage resistance.