Highly dispersive ammonium dimolybdate crystals with high purity have been prepared through reaction–evaporation–crystallization united route using commercial molybdenum oxide as starting material. The as-prepared ammonium dimolybdate uniform crystals were systematically characterized by X-ray powder diffraction, transmission-reflection optical microscope, Fourier transform infrared spectroscopy and TG-DSC thermal analysis. The Fsss grain diameter, loose packed density, and crystal-grain size distribution were also measured by the Malvern laser particle sizer. These collective characterization and analysis reveal that the ammonium dimolybdate grains are non-agglomerated uniform crystals with well normal distribution and geometric shape. The average Fsss diameter, d (0.5) and loose packed density are 433.316μm, 470.981μm and 1.592gcm −3 , respectively, which could well meet the quality requirements for the subsequent production of molybdenum powders.