Modification is mostly used to adjust and increase the performance of polymers by employing organic or inorganic fillers in composites. It is significant to investigate the functions of different fillers in polymer matrix. In this work, we prepared a series of composites by using polyurethane/acrylic dispersions as polymer matrix and nanofillers (cellulose nanocrystals, carbon nanotubes and aluminum oxide nanoparticles) as modifiers to study their micro-structure and applied performance. It is found that the different nanofillers can be dispersed in PUA homogenously, which are inclusive physically. Different nanofillers have a noticeable influence on the T g for the acrylate copolymers and the T g of the interphase between the acrylate and polyurethane. The CNTs significantly increases the elongation to 127.29%, and gives the highest dielectric response. We imply that the CNTs may be the most significant fillers to increase the mechanical and electrical properties.