Mo2N nanoparticles (4-15 nm) have been synthesized by ultrasonic dispersion of topotactic Mo2N crystallites in solution. Nanostructure is developed during topotactic conversion of MoO3 crystallites to porous Mo2N crystallites. These materials do not sinter during temperature-programmed syntheses up to 700 degrees C, The characteristic blue color of the dispersed Mo2N in aqueous solution is attributed to the surface oxide/hydroxide phase. Samples were characterized using TEM, X-ray diffraction, scanning tunneling microscopy, and BET surface area measurements.