Polycarbosilane-derived SiC fibers (CG Nicalon, Hi-Nicalon, and Hi-Nicalon type S) were exposed for 1-100 h at 1273-1673 K in air. Oxide layer growth and changes in tensile strength for these fibers were examined after exposure. The three types of SiC fibers decreased in strength as the oxide layer thickness increased. Fracture origins were located near the oxide layer-fiber interface. The Hi-Nicalon type S showed better oxidation resistance than the other polycarbosilane-derived SiC fibers after exposure in air at 1673 K for 10 h, This result was attributed to the nature of the silicon oxide layer on the surface of the SIC fibers.