The self-toughened Si3N4 ceramics where needle-like coarse ${eta}$-Si3N4 grains were dispersed within fine-grain-ed matrix were prepared via hot-prssing at 1730$^{circ}C$ for 2 h using 5 vol% ${eta}$-Si3N4 whiskers as a seed. In this study the microstructures and mechanical properties of self-toughened Si3N4 ceramics were investigated. The flexural strength of self-toughened Si3N4 ceramics was increased from 600-800 MPa of the Si3N4 monolith to 830-1025 MPa. The KIC was also increased from 4.0-5.0MPa$.$m1/2 of the Si3N4 monolith to 5.8-6.5MPa$.$m1/2$.$The needle-like coarse Si3N4 grains in self-toughened ceramics were considered to induce various toughening mechanisms including the crack deflection pull-out and bridging and to contribute to KIC improvement. In ad-dition to toughening mechanisms the KIC improvement was considered to be partially indebted also to the orien-tation of large ${eta}$-Si3N4 grains and to the promoting effect of ${eta}$-Si3N4 whiskers on the ${alpha}$ to ${eta}$ transtion.