Ca-α-sialons with low oxygen content were fabricated at 1800°C by hot pressing. The phase and microstructure were characterized by XRD and SEM. The calculated lattice parameter reveals that 20~30% Ca2+ ions still exist in the grain boundary phase of Ca-α′. A large amount of Ca-containing liquid phase efficiently promotes the anisotropic growth of α′ grains in Ca-rich composition. Reinforced only by elongated α′ grains, the fracture toughness of Ca-α′ can reach 4.96 MPa•m1/2.