After removal of the resin from PAN-carbon fibers, the fibers were coated with C or SiC by chemical vapor deposition (CVD) and the effects of these CVD coatings on the mechanical and chemical properties of carbon fibers were investigated. DTG analysis was conducted at different temperatures (993K, 1053K and 1113K) to establish the oxidation reaction models of the C/C or C/SiC coated fibers. The results showed that the CVD coatings enhance the oxidation resistance of the carbon fibers. The surface morphology of the CVD C or SiC fibers was investigated by SEM. The tensile strength of the fibers was found to decrease rapidly after CVD, while the Young’s modulus remained almost constant. These changes can be explained by the interface performance of the carbon fibers and the mechanism of CVD C or SiC deposition. The difference in dilatability between the CVD C or SiC layers and the carbon fibers was the main reason for the tensile failure.