The mechanical properties of SiC whisker, SiCw, reinforced β-Sialon composite were investigated. β-Sialon with 20 vol% SiCw showed excellent high temperature strength, 610 MPa at 1350°C, and fracture toughness, 5.3 MPa √m (Chevron Notched Beam, CNB, method). This fracture toughness value was an improvement of 75% over that of β-Sialon (monolithic material). This composite also showed excellent oxidation-resistance; the weight gain due to oxidation after 200 hr at 1350°C in dry air was 0.3 mg/cm2, and after oxidation the high temperature strength, 1350°C, was 683 MPa, an improvement over the pre-oxidation value. Also, in high temperature creep testing (200 hr at 1350°C and 300 MPa) deformation of the SiCw reinforced β-Sialon composite, SiCw/β-Sialon was 66% smaller than that of β-Sialon.