In this study, two types of nanoscale alpha-Al2O3 particles were used for preparation of alpha-Al2O3/thermoplastic polyurethane (TPU) composites. These alpha-Al2O3 particles were either coated or uncoated with stearic acid. For the uncoated alpha-Al2O3/TPU composite, the results of field-emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray spectrometry indicate that uncoated alpha-Al2O3 particles are significantly aggregated together. This aggregation is due to the poor compatibility between the inorganic filler (alpha-Al2O3) and the organic matrix (TPU). The size of clusters is in the range from 5 to 20 mu m. For the coated alpha-Al2O3/TPU composite, FE-SEM results indicate that most coated alpha-Al2O3 particles are well dispersed in the TPU matrix. This phenomenon results from the effect of surface modifier (i.e., stearic acid) on alpha-Al2O3 particles. Stearic acid can act as a compatibilizer to bridge the boundary between the TPU matrix and the alpha-Al2O3 particle. Stearic acid is not only, a suitable surface modifier for the nanoscale alpha-Al2O3 particle, but also a good dispersant for the dispersion of nanoscale alpha-Al2O3 particles in the TPU matrix. (C) 2008 Wiley Periodicals, Inc.