The Nb/Nb₅Si₃ In-Situ composite material strengthened with CNTs were prepared by Spark Plasma Sintering (SPS). The effects of CNTs content on microstructure and properties of Nb/Nb₅Si₃ in situ composites were investigated. The results show that the composite consists of Nb, α- Nb₅Si₃, and γ- Nb₅Si₃ phase. When adding over 2wt% CNTs, the new phase Nb₄C₃ was formed in the composites. The compressive strength and fracture toughness of composites increase obviously with increasing addition of CNTs. When the addition of CNTs is the 2wt%, the compressive strength and fracture toughness reached the maximum value and increased about 56%, 31% respectively. When the CNTs content added over 2wt%, the compressive strength fracture toughness decreased. The micrographs observed by SEM of fractography show the fracture appearance of the composites belongs to brittle cleavage fracture and partial intercrystalline fracture. The toughening mechanisms of composites are mainly due to the CNTs pullout and bridging.