By using {{{{ { { {Y }_{3 }Al }_{5 }O }_{12 } }} (YAG) and SiO2 as sintering additives the effect of the composition of sintering ad-ditives on microstructure and mechanical properties of the hog-pressed and subsequently annealed SiC ma-terials were investigated. Microstructures of sintered and annealed materials were strongly dependent onthe composition of sintering additives. The average diameter and volume fraction of elongated grains in an-nealed materials increased with the SiO2/YAg ratio while the fracture toughness increased with the SiO2/YAg ratio. The average MPa.{{{{ { m}^{1/2 } }} respectively. Typical strength and fracture toughness of an annealed material with SiO2/YAg ra-tionof 0.67 were 371 MPa and 5.6 MPa.{{{{ { m}^{1/2 } }} respectively.