Abstract: Superfine grinding is one of the effective techniques to change the microstructure and physicochemical properties of materials. In this study, the highland barley bran was selected as a raw material to prepare micropowder A and B, and then their microstructure and physicochemical properties were investigated to evaluate the processing feasibility of ultrafine powders for food supplements. Experimental methods, including laser particle size instrument (LPA), scanning electron microscope (SEM), thermogravimetric analysis (TG), differential scanning calorimetry (DSC), fourier transform infrared spectrometer (FTIR), X-ray diffraction (XRD) and rapid viscosity analyzer (RVA), were adopted to characterize the morphology and physicochemical properties of ground powders after superfine grinding. Moreover, many functional indexes were also evaluated during materials characterization, including chroma, resting angle, sliding angle, swelling force, packing density, compaction density, water solubility, water/oil holding capacity, cation adsorption capacity and the cholic acid adsorption capacity. Results show that the particle size of obtained bran powders gradually decrease, and powder textures are refined than before. The average particle size of coarse powders, micropowder A and B are 335.94μm, 72.52μm and 22.69μm, respectively. The maximum mass loss rates and temperature range of three types of barleybran powders indicate a slight difference in TG analysis. As the particle size decreases, the barley bran powders are more sensitive to thermal decomposition, while the thermal stability gradually decreases. FTIR confirmed that there was no new absorption peaks, and only relatively small changes in the intensity of the absorption peaks from two types of micropowders, when compared to the coarse highland barley bran powder. There was no position changes of main characteristic peaks, indicating that no chemical reaction occur in micropowder A and B. In XRD patterns, the diffraction peaks of 2θ at 16° and 18.8° show that the remained starch in the highland barley bran is A type crystalline, and the diffraction peaks of 2θ at 20.18°, 34.05°, 22.9°, and 18.8° are ascribed to the cellulose type I starch. The peak characteristics weaken with the decrease of particle size, as well the width of half peaks and the intensity of peaks in the diffraction patterns. Furthermore, there are also some changes in the enthalpies and peak temperatures of different powders after superfine grinding treatment, indicating that the enthalpies of coarse powder, micropowder A and B increase from 23.89 J/g to 32.95J/g. Gelatinization temperatures of slightly ground highland barley bran increase, whereas the initial temperature, peak temperature and the final temperature have a significant impact on the thermodynamic properties of the fine-powdered highland barley bran. As the grain size of highland barley bran decreases, the viscosity of obtained powders increases, including peak viscosity, valley viscosity, final viscosity and disintegration value. Superfine grinding treatment can reduce the regrowth value of highland barley bran. With the decrease of the grain size, the resting angle, sliding angle, adsorption water and oil holding capacity, expansion force, vibration density, accumulation density and cation exchange capacity of the fine powders also significantly reduce, indicating that superfine grinding can change the microstructure and physicochemical properties of residual starch in highland barley bran. This study can provide a theoretical basis and technical support to improve the full utilization of highland barley bran, and thereby to transfer micronized highland barley bran powders to serve as the food supplemental materials.