High temperature strength, creep and creep-fatigue behavior were investigated in air for Al₂O₃, SiC and Si₃N₄ ceramics. The high temperature tensile strength was influenced by the existence of additives in ceramics. The tensile strength showed displacement rate dependence. In the creep-fatigue tests of Si₃N₄ at 1673K, not only hysteresis loops but also ratchetting behavior were observed in the stress-displacement curves. It seemed that the fracture occurred when the total plastic ratchetting deformation reached a constant value.