The scanning Maxwell stress microscope (SMM), a new type of scanning force microscope, has been developed to facilitate the observation of electrostatic features of organic and inorganic thin films and surfaces with nanometre-level resolution. The SMM is in principle an extension of the traditional Kelvin method for surface potentiometry, but, in contrast with the original Kelvin method measuring the electric current, relies on the detection of the electric-field-induced oscillation of a cantilever. The SMM is capable of simultaneously imaging the surface potential and the combined information on dielectric constant and topography for thin film samples. depending only on the harmonic analysis of the field-induced oscillation. We have implemented the SMM based on a commercially available atomic force microscope and have favourably confirmed its performance for lithographically prepared microstructures, indicating a lateral resolution of about 100 nm with a sensitivity in surface potential of less than 1 mV.