Abstract: Non-agglomerated ammonium dimolybdate (ADM) monocrystals with large diameter and high dispersion were prepared through reaction-evaporation-crystallization united process using ammonium tetramolybdate and ammonia solution as starting reactants.Structure and morphology of the prepared ADM samples were characterized by X-ray powder diffraction，Fourier transform infrared spectroscopy，and transmission-reflection optical microscope.The thermal decomposition process of ammonium dimolybdate was deduced by TG-DSC thermal analysis,and Fisher particle size,size distribution,and loose packed density were tested by Malvern dry powder laser particle sizer.It is shown that the prepared ADM samples were non-agglomerated monocrystals with well grain normal distribution and geometric shape,and the Fisher particle size,d(0.5)，and loose packed density were 433.316 μm，470.981 μm,and 1.592 g/cm³,respectively.

Key words: ammonium dimolybdate, monocrystal, ammonium tetramolybdate