Polymers have become more and more attractive to acoustical science and technology. Recently, large electric-field-induced strain responses in segmented polyurethane elastomers have drawn the wide attention of many researchers due to their promising applications in sensor, actuator, and microelectromechanical system (MEMS) devices. Mechanisms of the large strain responses were investigated by studying elastic, dielectric, and electromechanical properties as functions of temperature, frequency, and sample thickness. The effects of the injected charges on the large electric-field-induced strain coefficient in electrostrictive polyurethane thin films were also studied using the thermally stimulated discharging current (TSDC) technique. It was found that the contributions to the field-induced strain responses are associated with intrinsic electrostriction and the Maxwell stress effect. These effects can be enhanced by distribution of the injected charges, which results in a modified nonuniform internal electric field profile in the region near the polymer--electrode interface. In addition, transitional phenomena related to the molecular motions of soft segments and hard segments of the segmented polyurethane play an important role. The experimental results will be presented and discussed. The achievements will supply a guideline to develop new and better polymer materials for electromechanical and acoustical applications.