For the first time a light-induced local modification of the surface potential of an azobenzene-containing film in the near field of a scanning force microscope tip has been observed. The modification occurred when the tip was scanned a fixed distance from the surface (in noncontact mode) while simultaneously irradiating the sample with light of low intensity. The locally modified regions are detected as areas with more negative surface potential. The smallest size of these areas is several hundred nanometers with a difference in surface potential of a few hundred millivolts. No alterations in topography were observed.