The mechanical properties of antimony-doped tin oxide (ATO) nanoparticle/poly (vinyl acetate-co-acrylic) (PVAc-co-acrylic) coatings with various ATO contents were investigated using depth-sensing indentation. These coatings were prepared from aqueous dispersions of ATO and PVAc-co-acrylic latex. Three types of methods, including a prolonged load holding time, analysis of the pull-off portion of the unloading curve, and dynamic indentation, were used to characterize the mechanical properties of these composite coatings. As compared to dynamic indentation, quasistatic conventional indentation even with a prolonged load holding time and analysis of the pull-off portion of unloading curves generate more scattered coating modulus data. This is due to the effect of creep deformation and inconsistency of the pull-off portion dimension, respectively. The results obtained using dynamic indentation are more reliable because the technique minimizes the effect of creep deformation using a combination load including static and dynamic components. The dynamic indentation results indicate that the addition of the ATO nanoparticles made the composite coatings stiffer and more elastic solid-like. For example, the storage indentation modulus of the PVAc-co-acrylic coating is similar to1 GPa and tan delta is similar to1.6; the addition of 0.50 volume fraction of ATO increased the modulus to similar to5 GPa and reduced the tan delta to similar to0.01. (C) 2005 Society of Plastics Engineers.