Using pure Nb and Nb5Si3 metal powder as raw material, Nb/Nb5Si3 alloys with three different proportions (90:10, 70:30 and 50:50) were fabricated by spark plasma sintering (SPS). The microstructures, relative densities, and room-temperature mechanical properties of the three SPS Nb/Nb5Si3 alloys were investigated. It is revealed that the synthesized alloys are composed of two phases of Nb and Nb5Si3. The volume fraction of Nb and Nb5Si3 in the synthesized alloys is in line with the original ratio, indicating that the volume fraction ratio of Nb to Nb5Si3 is able to be precisely controlled. The SPS Nb/Nb5Si3 alloys are nearly fully dense and their relative densities are above 99.66%. With an increasing volume fraction of Nb5Si3, the room-temperature hardness of the bulk SPS alloys increased, meanwhile, the fracture toughness decreased with a little amplitude. The SPS alloy with a Nb/Nb5Si3 volume fraction ratio of 50:50 has the highest hardness of Hv879.6, and that with a Nb/Nb5Si3 volume fraction ratio of 90:10 has the highest fracture toughness of 6.9MPa m1/2.