The mechanism of ESD (electron stimulated desorptions) has been experimentally examined for organic molecules on Al and Au by irradiating the surfaces with middle energy (0.5 to 3.0 keV) electron beams. ESD of neutrally desorbed molecules has been observed in a UHV chamber installed with a SEM/AES and a 0-mass spectrometer. ESD molecules from adsorbed polystyrene or rosin are measured from a practical view point. It is found that ESD efficiency depends upon the incident electron energy and molecular species, and there are three different ESD desorption mechanisms, i.e., direct and indirect ESD mechanisms and electron induced thermal desorption. It is concluded that the present method of ESD using middle energy electron beams is of practical use to analyze the surface organic contaminants in submicron areas.