Nanocrystalline niobium nitride (NbN0.9) was successfully synthesized at 600 degrees C through a solid-state reaction. The synthesis was carried out in an autoclave by using NbCl5 and NaN3 as the reactants. The X-ray powder diffraction pattern indicates the formation of cubic NbN0.9. Transmission electron microscopy images show that typical NbN0.9 crystallites are composed of uniform particles with an average size of about 30 nm and nanorod crystallites with a typical size of about 40 x 2500 nm. Magnetic measurements exhibited that a superconducting transition occurred at 15.4 K for the NbN0.9 product.