Polyurethanes (PU) have demonstrated their ability to convert electrical energy into mechanical energy and vice versa. The incorporation into a PU matrix of nanofillers, such as carbon nanotubes (CNT), can even enhance the actuation and the harvested energy performances. However, it is well known that CNTs are hardly dispersed in a polymeric matrix, and that the interfacial adhesion strength is generally poor. Moreover, the improvement of electromechanical properties is limited by the low volume fraction of CNT that can be dispersed because of their low percolation threshold. In this study, we present how grafting polymer onto CNTs can improve the physical properties of PU nanocomposites and accordingly the electromechanical properties of the PU/grafted CNT nanocomposites, compared to those of pristine PU. The dielectric permittivity is largely increased and the percolation threshold is found around 5 vol.%. Measurements of the thickness strain under an applied electrical field demonstrate a twofold increase of the electrostriction coefficient. The energy harvesting properties investigated by monitoring the evolution of the current under a DC electric field are also enhanced.