Ti5Si3 matrix composites reinforced by carbon nanotubes were fabricated by vacuum hot pressing sintering. X-ray diffraction and scanning electron microcopy were carried out to analyze the phase and microstructure of the composites. The effects of carbon nanotubes on mechanical properties were investigated. Experimental results showed that the nanotubes partly reacted with Ti and Si powders to obtain Ti5Si3 and Ti3SiC2, TiSi2 when the sintering temperature is about 1380oC. The mechanical properties of composites can be affected by carbon nanotubes. Meanwhile, the maximal increments of Vickers hardness, bending strength and fracture toughness of the composites, compared with the Ti5Si3 matrix, were 62.9%, 160.9% and 159.3%, respectively. Both of transgranular and intergranular fracture in the composites were the main fracture mode. The fracture manners of composites mainly include “bridging” of CNTs, “deflection” of minor phases and the evolution of grain.