Nb-20Si, Nb-20Si-10W and Nb-20Si-10W-10Mo samples were prepared by a spark plasma sintering (SPS), the effects of W and W-Mo additions on the microstructure of Nb/Nb5Si3 composites were mainly investigated. The microstructures were examined by scanning electron microscope (SEM). X-ray diffraction (XRD) was used for phase identification of the samples. The compositions were analyzed by electron-probe micro-analysis (EPMA). Results indicate that Nb/Nb5Si3 composites up to 99.59% of theoretical density are fabricated. W can be perfect solid-solutioned in Nb/Nb5Si3 composites, and the microstructure of Nb/Nb5Si3 composites is not changed, but the microstructure of Nb/Nb5Si3 composites is obviously changed after addition of W-Mo, Nb monophase, the solid solution of W and Mo in Nb, and the solid solution of partial Nb in W appear, but the solid solution phenomena of Nb5Si3 is not detected.