In this study, two types of nanoscale alpha-Al2O3 particles were used to prepare alpha-Al2O3/Nylon 6 nanocomposite masterbatches. They were either uncoated or coated with stearic acid. A wide angle X-ray diffractometer was used to examine the crystal structure of virgin pure nylon 6 and alpha-Al2O3/nylon 6 nanocomposite masterbatches. Meanwhile, a differential scanning calorimeter and a thermogravimetric analyzer were used to illustrate the influence of nanoscale alpha-Al2O3 particles on the thermal properties of the alpha-Al2O3/nylon 6 nanocomposite masterbatches. In addition, a field-emission scanning electron microscopy was applied to reveal the dispersion of uncoated or coated alpha-Al2O3 particles in the nylon 6 matrix. Furthermore, an energy dispersive X-ray spectrometer was also conducted to confirm the existence of the aluminum element in the alpha-Al2O3/nylon 6 nanocomposite masterbatches. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112:1063-1069, 2009