Wool powder was produced from wool fiber by pretreatment and then ground by a specially designed machine. Scanning electron micrograph (SEM) photos show that ultrafine wool powder around 2 mum in diameter can be produced from fiber around 25 ttm in the diameter, and most of the powder is in the form of needles. The powder can be widely applied in new biomedical material development and cosmetic products. Thermal analysis of thermogravimetry (TG) and differential scanning calorimetry (DSC) show that the temperature for moisture evaporation in the powder was elevated to around 150degreesC from the control wool fiber, which was around 120degreesC. As the powder particle size decreases, the temperature corresponding to the crystal cleavage and the destruction of the crosslinkages increased, which is perhaps mostly due to the new crosslinks and new crystal that were produced during powder processing. The temperature for the liquefaction was also elevated and the relative TG results show that the last residue of the powder after 600degreesC is higher than that of the control sample. The thermal results show that as the powder particle size decreases, the thermal stability increases slightly. (C) 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2372-2376, 2003.