Abstract: The morphology and microstructure of a 3D carbon/carbon composite, and the corresponding composites doped with refractory metal carbides, were studied by SEM and TEM after ablation tests at various conditions. Results showed that in the case of composites doped with refractory metal carbides, the carbon fibers in the Z-direction were ablated faster than the matrix carbon. The bigger the difference of ablation rate between the carbon fibers and the matrix carbon, the greater the ablation rate of the bulk material. In contrast, in the carbon/carbon composite, the matrix carbon at the interface region was ablated faster than the carbon fibers. Micro-crystalline growth of carbon fibers and formation of columnar shaped carbon in the matrix carbon were commonly observed. Ablation conditions had a great influence on the morphology and the ablation mechanism.