Lu2O3 and SiO2 were used as sintering additives and rod-like β-Si3N4 seeds were added to enhance β-Si3N4 grain unidirectional growth. Silicon nitride ceramics were prepared by tape casting and gas pressure sinteringat 1950oC in 10 atm nitrogen atmosphere for 6 h. Compare to the no-seeded Si3N4, the seeded and tape-cast Si3N4 ceramics have obvious anisotropic microstructure and anisotropic properties. When a stress applied along with the grain alignment direction, the bending strength of the seeded and tape-cast Si3N4 at 1500oC was 738 MPa, which was almost the same as its room temperature bending strength. However, the bending strength of the seeded and tape-cast at room temperature was 556 MPa (perpendicular direction); and their thermal conductivity were 67 W/m·K (perpendicular direction) and 83 W/m·K (parallel direction), respectively. The anisotropic properties of the seeded and tape-cast Si3N4 were attributable to the elongated Si3N4 grain alignment.