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In order to enhance the fracture toughness of mullite,three-dimensional braided carbon fiber reinforced mullite (C/mullite) composites were prepared using the Al2O3-SiO2 sol with a high solid content as raw material.Mullitization behavior of the sol was characterized.Then,the microstructure,mechanical properties and oxidation resistance of C/mullite composites were investigated.It is found that the SiO2-rich mullite with desirable sintering shrinkage can be synthesized at 1 300 ℃ from the sol with an Al2O3/SiO2 mass ratio of 1∶1.The C/mullite composites with a total porosity of 21.5％ were fabricated by repeating 18 cycles of vacuum impregnation-drying-heat treatment,showing a flexural strength of 234.5 MPa and a fracture toughness of 13.1 MPa.m1/2.Since carbon fibers were protected by compact matrix,the C/mullite composites show favorable oxidation resistance during 1 200 ℃-1 600 ℃ even if an open porosity of 10.3％ was detected.