Hi-h resolution imaging of the organic monolayer film in an ambient condition by dynamic force microscopy (DFM) utilizing the frequency modulation (FM) detection method was demonstrated. Although the mechanical Q-factor of the cantilever used was about 1000. we could image molecular rows in the monolayer film whose pitch was about 2 nm. The image was not clear probably due to the adsorbed water layer on the film. Furthermore, we also demonstrated the operation of the FM detection method in liquid with mechanical excitation of the cantilever by using a PLL circuit with a narrow operating range. (C) 2002 Elsevier Science B.V. All rights reserved.