Most of fracture processes of carbon/carbon composites (C/Cs) have been found to profoundly affected by their interfacial properties. A fiber-bundle pull-out test is utilized to determine the interface strength between fiber bundles and matrix of two kinds of C/Cs. Pre-fracture observations revealed that amount of voids and gaps existed in the interface, which make the interface strength decreases. The interfacial shear strengths of two kinds of C/Cs were all very low. Post-fracture observations revealed that a shear fracture was successfully induced within the carbon matrices at the loaded fiber bundle interface.