To obtain a dense SiCf/SiC composite by the chemical vapor infiltration (CVI) process, whisker growing before matrix filling was applied, which is called the whisker growing assisted CVI process. The whisker growing and matrix filling processes were carried out using MTS (CH3SiCl3) and H2 as source and diluent gases, respectively. Tyranno-SATM was used as a reinforced substrate. Characterizations of SiC whisker grown during the in situ whisker growing process have been investigated. The weight gain rates with the matrix filling time and the density of composites was measured. The flexural strength with the thickness of the pyrolytic carbon (PyC) interlayers has been evaluated. b-SiC whiskers with many stacking faults were grown well in the Tyranno SATM fabrics. Tyranno-SA/SiC composite with a PyC interlayer thickness of 150 nm had a flexural strength of 610 MPa and the density of 2.71 g/cm3.