The influence of high temperature oxidation time on the composition, microstructure, and mechanical and electrical properties of MoSi2 RSiC composites was discussed. The experimental results show that the oxidation of composites mainly formed a dense cristobalite SiO2 film on the external surface. The mechanical properties of the composites increased and then decreased with the increase of oxidation time, and MS 2.62 oxidized for 40 h achieved the maximal flexural strength and elastic modulus of 146.03 MPa and 239.49 GPa, respectively. Meanwhile, the mechanical properties of composites were still greater than those of samples without any oxidation even after 100 h oxidation. With the increase of oxidation time, the volume resistivity of MoSi2 RSiC composites decreased and then reached a flat, while the volume resistivity of MS 2.62 was about 50 mΩ·cm after 100 h oxidation, which was about 42% lower than its original values. Additionally, the calculated influence factor I indicated that this variety might be caused by the healing of micro crack at the interface between RSiC and MoSi2 induced by the plastic deformation of MoSi2, resulting in the decrease of the volume resistivity of composites.