In this study, the silk treated by steam explosion was pulverized into fine powder with a mean particle size of 1.829 mu m, then the feasibility of the application of the protease treatment to produce finer and more uniform silk powder was investigated. The results indicated that after the enzymatic treatment, the mean diameter of the silk powder was reduced from 1.829 to 1.546 mu m and the equivalent diameter distribution became more concentrated; thus, the uniformity of the particles was improved. The infrared spectra analysis demonstrated that the silk powder remained the beta-sheet crystalline structure. X-ray diffraction analysis showed the crystallinity of the polished silk powder was very slightly strengthened. It was found that the treatment reduced some polar amino acid in the sericin; however, the composition of the kinds of the amino acids did not change. In addition, the hot water-solubility and moisture regain of the polished silk powder declined very slightly. (c) 2006 Wiley Periodicals, Inc.