In order to investigate the relations between microstructures and properties of SiC fibers, SiC fibers are annealed in air and Ar respectively at elevated temperatures in this study. The strength of SiC fibers annealed in air decreases as the temperature increases above 1100℃. When the temperature reaches 1 200℃, bubbles are formed in the silica layer. The strength of SiC fibers annealed in Ar decreases gradually as the temperature increases above 1100℃, while decreases sharply as the temperature increases above 1500℃. accompanied by the transition of β-SiC to α-SiC and the enhancement of SiC grain size