Abstract: Nb/ Nb₅Si₃ is a new high temperature st ructural composite and has great application potentials in manyfields. In order to decrease the fabricating cost of Nb/ Nb₅Si₃ composite and to efficiently cont rol it s microst ructure ,spark plasma sintering (SPS) technology was used to in2si tu synthesize Nb/ Nb₅Si₃ composites from a mixture of Nband Si powders , and the effect of Si content on the microst ructures of the fabricated composites was mainly investi2gated. The result s show that fully dense Nb/ Nb₅Si₃ composites can be fabricated by SPS technology , and the micrO₂st ructures of the composites consist of the in2si tu synthesized Nb₅Si₃ and the dispersed Nb particles. Moreover , withthe increasing of Si content from 6 % to 20 %(atom f raction) , the volume f raction of the synthesized Nb₅Si₃ in thecomposites increases , whereas the content and size of Nb particles decrease obviously. As a result , the density andhardness of the composites are both improved.