Collecting the vibration energy existing in the surrounding environment and its transformation to a useful electrical energy in order to supply ultra-low power systems remains an emerging and promising technology. During the last decades, most of research efforts dealt with energy-harvesting technology using piezoelectric ceramics. However, those materials are stiff and limited in mechanical strain abilities. In addition, they lose their stiffness and piezoelectricity at high levels of mechanical strain. Thus, they are unsuitable for many applications in which low frequency and high strain level are required. However, electrostrictive polymers are lightweight, very flexible, have low manufacturing costs and are easy to mould into any desired shapes. These special properties led to them being considered as potential actuators. However, it is not well known that these materials also can be used for mechanical-to-electrical energy harvesting. In this research paper, electromechanical characterization of polymer/lead zirconate titanate composites was extended. The first part develops the analytical model predicting the energy harvested by polyurethane/PZT composites from electrical and mechanical properties of their constituent materials. Indeed, this model was based on the approach of representing the experimental setup with an equivalent electrical scheme. The second part focuses on the assessment of model performance by comparison between predicted and observed values. As a result, good agreements were observed between the two sets of data; in addition, the model could be used to optimize the choice of constituent materials. The last part concerns the contribution of both the electrostrictive effect and piezoelectric effect in electrical powers harvested by PU/PZT composites.