Nano-SiCp/MoSi2 composites with different SiC volume fraction have been synthesized by in situ reactive hot press sintering with the milled Mo, Si and C elements powders. The X-ray diffraction (XRD) detection shows the composites are composed of α-MoSi2 and β-SiC, and transmission electron microscopy (TEM) shows that the particle sizes of β-SiC formed by in situ reaction are in range of 20-100nm, and most of the them locate in grain boundary and some particles embed in MoSi2 grain. The isothermal oxidation and thermal cycling test of nano-SiCp/MoSi2 composites were carried out in air at temperatures of 500°C. The pest phenomenon was not found during oxidation and cyclic oxidation at 500°C for 500 hours and 50 cycles, respectively. All the composites have both excellent oxidation resistant and good cyclic oxidation resistant. The mechanisms of oxidation at low temperature were discussed also.