Unidirectional C/SiC composites were successfully prepared by hot pressing at 1850 degrees C under 20 MPa, using different fiber volume fractions (from 28 vol% to 55 vol%) as reinforcement. The densification process of the composites became increasingly difficult with increasing fiber volume fraction, and some small pores were still distributed in the intrabundle regions of the composites. The cracks, resulting from the residual thermal stress in the composites due to the mismatch of the thermal expansion coefficient of the matrix and the fiber, were distributed in the matrix. With the increase of fiber content, the mechanical properties of the composites could be improved and the composites exhibited an obvious noncatastrophic fracture behavior due to a decrease in the thermal residual stress and an increase in the fiber pull outs.