The interest in aqueous-based resins for various applications such as coating or in the pharmaceutical field has recently increased due to the need for constant cost reductions and the necessity to control emissions of volatile organic compounds. As most polymers used in these applications are water insoluble, aqueous- based resins generally contain particles in suspension. The average particle size and size distribution are essential data on which the stability and properties of the dispersions depend [1]. Light scattering and cryo-transmission electron microscopy (cryo-TEM) have proved to be complementary techniques to characterise various natural [2] or synthetic [3] polymer nanoparticles dispersed in water. Light scattering is non-destructive and provides fast measurements in a wide range of particle size. However, it cannot analyse double populations, large distributions, absorbent materials, or mixtures of substances with different densities [4]. In this study, cryo-TEM and image analysis were combined to characterise a variety of aqueous polyurethane dispersions. The results were compared with those obtained from dynamic light scattering (DLS) experiments.