Owing to their low density and good mechanical properties at high temperatures, C/SiC composites are increasingly used in the aerospace industry. They are also being proposed as thermal-structural materials in the hypersonic field; however, C/SiC composites are easily oxidized in high-temperature air environments. In this study, a C/SiC composite was coated with a SiC-ZrC oxidation-resistant layer by a two-step sintering method using Si-25%Zr (mass fraction) alloy, and the phase evolution of the coating was studied during the sintering. The oxidation resistance of the material was then tested at 1400^oC in an air environment. The microstructural changes of the coating before and after oxidation and the effect of oxidation on the bending properties of C/SiC were analyzed. After the reaction with carbon, Si and ZrSi₂ disappear in the coating, leaving only pure ZrC and SiC. The ZrC phase refined the structure of the reactive SiC layer. The grain size of the sintered SiC was 2 μm, versus 5-20 μm for SiC sintered from pure Si. The refined grains created a dense and continuous SiO₂ film during the oxidation process. As the oxidation time was increased at 1400^oC, the C/SiC composite with the SiC-ZrC coating began losing weight at 200 s, but began gaining weight at 500 s as a dense SiO₂ film was formed. After 1000 s of oxidation, the flexural strength of the C/SiC composites was 335 MPa, only 5% lower than that of the initial C/SiC composite. According to this result, the sintered SiC-ZrC oxidation-resistant film effectively protected the mechanical properties of the C/SiC composite during the oxidation process.