Bis-maleimide (BMI) resins are widely applied in carbon fiber reinforced polymer composites in aerospace fields, for their excellent thermal and mechanical properties. The effects of thermo-oxidative aging on mechanical properties of carbon fiber reinforced BMI composites were investigated by SEM with the combination of flexural strength test and inter-laminar shear strength (ILSS) test. The results indicated that the thermal-oxidative aging had some effects on mechanical properties of carbon fiber/BMI composites; however the testing temperature or service temperature had much more effects than aging time. With aging time increased, the flexural strength at 150 oC and the ILSS at 25 oC slightly increased, while the ILSS at 150 oC decreased gradually. Both test results of mechanical properties and fracture models of damaged flexural specimens by SEM indicated that the matrix resin in the composites showed some viscoelastic behaviors that resulted in the remarkable dependence of mechanical properties of the composites on temperature. Therefore, the carbon fiber reinforced BMI composites had lower flexural strength and ILSS at 150 oC than that at 25 oC.