Polyurethane (PU) exhibit very high electromechanical activity, and has a great interest for a wide range of transducer and actuator applications. It has been recently pointed out that this strong electrostriction may result from the phase separation. In the present work, a model taking account the PU nanostructure is presented. In order to validate this model, three PUs of similar compositions but different soft segment fractions have been characterized by DSC, TEM, AFM and SAXS and their electrostriction properties have been measured. When taking into account the diameter of the hard domains (HD) and the HD HD distance, it is found that the model proposed well reproduces the experimental electrostriction properties of these phase-separated PUs. (C) 2015 Elsevier Ltd. All rights reserved.