The synthesis of Ti3SiC2/SiC composites was studied by testing 3TiC+2Si or 3TiC+2.2Si + xAl (x = 0 or 0.2) as sintering mixtures. In order to reveal the mechanism of reactive sintering of Ti3SiC2/SiC composites, the mixtures were sintered either by pressureless sintering or by sintering under pressure between 1200 °C and 1500 °C during 15min. The results showed that the nucleation of SiC grains occurs first at the surface of the TiC grains, limiting therefore the progression of the conversion at 1200 °C and 1300 °C. Silicon defects are the main limitation of the synthesis of Ti3SiC2/SiC composites because of volatilization and molten silicon losses. The addition of aluminum promotes the conversion by reacting with oxygen and resulting in the formation of Al2O3 at the grain boundaries. The optimum experimental parameters for the synthesis of Ti3SiC2/SiC composites were determined to be a TiC/Si/Al molar ratio of 3/2.2/0.2 maintained at 1500 °C for 15min.