An ultra-fine Nb-Silicide in situ composite whose nominal composition is Nb-16Si-10Ti-10Mo-5Hf was fabricated by mechanical alloying followed by spark plasma sintering. The microstructure consists of an Nb solid solution, Nb₅Si₃ and a small amount of Nb₃Si with all three phases being in the sub-micro range. This in-situ composite exhibits good balance of strength between ambient temperature and high temperature; the ultimate tensile strength is 413 and 496 MPa at room temperature and 1200oC, respectively. The tensile fracture behavior is dominated by cleavage of the Nb₅Si₃ phase at 1200oC and lower temperatures. However, the fracture behavior is governed by ductile rupture of Nbss at 1300oC and higher temperature, which would be ascribed to both the increased ductility of Nbss and the decreased interface strength. At 1400oC and higher temperature, the material exhibits extensive plasticity or superplasticity; the dominant deformation mechanism is grain boundary at 1400oC and higher temperature.