In this article, we introduce a new Method, Mie scattering, for investigating the dependence of the morphology of polypropylene (PP)/polystyrene (PS) blends on the composition and mixing time. The size and corresponding distribution of the particles were also deduced on the basis of the Mie scattering theory. To confirm the effectiveness of this new method for morphology studies, scanning electron microscopy (SEM) vas employed to Study the morphology development as a function of the blend composition and mixing time; furthermore, the results by Mie scattering were compared with those by SEM analysis. The results by Mie scattering were similar to those by SEM, and this indicated that Mie scattering is an effective method for describing the morphology development of polymer blends. The main purpose of this article is simply to report this new method; in another article of this series, the application of this method in investigations of the compatibilization of PP/PS blends will be reported. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 116: 1933-1939, 2010