The influence of the fiber/matrix interlayers on the mechanical properties of T800-HB fiber (a kind of carbon fiber) (the fibrous is three-dimensional four-directional braided) reinforced silicon carbide (SiC) matrix composites has been evaluated in this paper. The composites were fabricated through PIP process, and SiC layers were deposited as fiber/matrix interlayers by the isothermal CVD process. Fiber/matrix debonding and relatively long fiber pullouts were observed on the fracture surfaces. The mechanical properties were investigated using three-point bending test and single-edge notched beam test. The T800-HB/SiC composites exhibited high mechanical strength, and the flexural strength and fracture toughness were 511.5MPa and 20.8MPa•m1/2, respectively.