Single-walled carbon nanotube (SWCNT)/SiC composites were successfully prepared by direct thermal decomposition of polycarbosilane (PCS) precursor. The SWCNT/SiC composites were prepared by the hot-pressing the SWCNTs-PCS (7:3 mass%) mixture at temperatures of 1000, 1400 and 1800°C under a pressure of 120 MPa. The effects of SiC synthesis and processing temperatures on the mechanical properties of the resultant composites were investigated by comparing the experimental data obtained from the SWCNT/SiC composites and the binder-free SWCNT solids. The XRD and TEM-EDS analyses revealed that the β-SiC was successfully prepared through direct thermal decomposition of PCS precursor. The specific modulus and strength of the SWCNT/SiC composites were always about 8 GPa/Mg/m3 and 20 MPa/Mg/m3 higher than those of the binder-free SWCNT solid under identical processing temperatures. Such remarkable stiffening and strengthening by SiC synthesis may be due to the load-transfer efficiency of SWCNTs in the SWCNT/SiC composites.