Astragalus membranaceus is a common traditional Chinese medicinal plant widely used as a tonic to enhance the body's natural defense mechanisms. The objective of this study was to investigate the application of the superfine grinding technology in A. membranaceus. The physical-chemical properties of five types of A. membranaceus powders with particle sizes of 300, 149, 74, 37 and 7.56 mu m were investigated. The experiments showed that the smaller the A. membranaceus particle dimension was, the greater the surface area (from 0.191 to 1.573 m(2)/g) and bulk density (from 0.5139 to 0.6139 g/ml) was, the smaller the angles of repose (from 52.30 degrees to 35.63 degrees) and slide (from 47.37 degrees to 29.47 degrees) were. The water holding capacity (WHC) and polysaccharide solubility significantly improved as decreasing the size of A. membranaceus particle (p < 0.05). SEM images revealed the shape and surface morphology of five types of A. membranaceus powders. (C) 2010 Elsevier B.V. All rights reserved.