A method to characterize the vibrating shape of a bimorph deformable mirror by measurement using a laser displacement sensor is presented. The displacement of the deformable mirror surface at a point is recorded as a frequency response function. The surface profile is synthesized from the response functions obtained at multiple points on a deformable mirror by postprocessing. The method has a wide frequency range and high-frequency resolution, suitable to investigate the resonance behavior of a deformable mirror. Although the spatial resolution is low compared with an interferometer, it is sufficient to identify low-spatial-order shapes at resonance frequencies. The accuracy of the displacement measurement is estimated to be comparable with interferometric data.