Alumina /poly(ethylene terephthalate) nanocomposites were prepared by melt compounding with a twin-screw extruder. The melt temperature, screw rotation speed, and feed rate were selected as important processing parameters, and their effects on the degree of mixing were studied with full-factorial, two-level experimental design. To quantitatively assess the effects of the processing parameters, the degree of mixing of the nanocomposites was evaluated by the skewness of the quadrat method based on the number of particles in transmission electron microscopy images. The screw speed was found to be the most important processing parameter controlling the degree of mixing under the conditions in this investigation. The specific energy input (SEI), related to the shear intensity, was found to correlate closely to the degree of mixing. The degree of mixing improved with increased SEI up to a limiting value, termed the critical SEI, indicating that there may be a critical value required for the optimum dispersion of a given system. A modeling approach was proposed to determine the critical SEI needed for complete mixing. Initial results showed that the critical SEI predicted by this model was within a factor of 3.5 of that obtained experimentally, demonstrating the utility of this approach for the dispersion of nanofillers. (C) 2008 Wiley Periodicals, Inc.