Three types of polycarbosilane-derived SiC fibers (Nicalon, Hi-Nicalon, and Hi-Nicalon S) with different SiO2 film thicknesses (b) were subjected to exposure tests at 1773 K in an argon-oxygen gas mixture with an oxygen partial pressure of 1 Pa. The suppression effect of a SiO2 coating on active oxidation was examined through TG, XRD analysis, SEM observation, and tensile tests. All the as-received fibers were oxidized in the active-oxidation regime. The mass gain and the SiO2 film development showed a suppression of active oxidation at b values of greater than or equal to0.070 mum for Nicalon, greater than or equal to0.013 mum for Hi-Nicalon, and greater than or equal to0.010 mum for Hi-Nicalon S fibers. Considerable strength was retained in the SiO2-coated fibers. For Hi-Nicalon fibers, the retained strength was 71%-90% of the strength in the as-received state (2.14-2.69 GPa).