The mechanical characterization of single micron-sized polymer particles is very important for understanding the anisotropic conductive adhesives interconnection. In this article, a nanoindentation-based flat punch method was employed to investigate the mechanical properties of single polymer particles. A diamond flat tip, instead of a commonly used sharp tip for indentation, was specially designed to deform single polymer particles. The maximum applied load is 10 mN and the linear loading/unloading rate is 2 mN/s. Two types of amorphous polymer particles were examined. The polymer particles display significantly different stress-strain behaviors. The material responses at different strain levels were analyzed and compared. A particle size effect, the smaller the diameter, the harder the particle, on the compression stress-strain behavior, was observed. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 1398-1405, 2009