Fully dense samples of TiB2-TiCX and TiB2-TiCX/15SiC ceramic composites were fabricated by in-situ synthesis under hot isostatic pressing from TiH2, B4C and SiC powders. Their oxidized behaviors at different temperatures were tested. Optical micrograph studies and thermo-gravimetric analyses show that the highest effective temperature of oxidation resistance is 700°C for TiB2-TiCX, and 1100°C for TiB2-TiCX/15SiC. The weight gain of TiB2-TiCX/15SiC below 1100°C is quite low, and it rises up suddenly when the temperature reaches 1200°C. Thus, the highest effective temperature of oxidation resistance is 1100°C for TiB2-TiCX/15SiC. The oxidation dynamic curves of TiB2-TiCX/15SiC ceramics accord with the parabola’s law. The activation energy of TiB2-TiCx/15SiC (189.87kJ.mol-1) is higher than that of TiB2-TiCx (96.44kJ.mol-1). In the oxidation process of TiB2-TiCx/15SiC, TiB2 reacts with oxygen and generates TiO2 and B2O3 at first. A layer of whole homogeneous oxide film cannot be formed, in the mean time, the oxidation of TiC begins. When temperature goes up to 1000°C, TiC phase is totally oxidized. SiC is oxidized to SiO2 at about 900°C, Meanwhile, TiO2 forms denser film than B2O3, which grows and covers the surface of the material, and gives better property of oxidation resistance.