The exoelectron emission participating in catalytic reactions on nickel oxide film was investigated using a Geiger counter with an argon-ethanol counting gas. The thermally stimulated exoelectron emission (TSEE) from the metal oxide surfaces was related to the chemical and electrical nature of the surfaces characterized by means of x-ray photoelectron spectroscopy, x-ray diffraction, and surface potential (SP) measurement. Three different metal oxide samples were prepared : metal sheets oxidized by heating in air at various temperatures, and subsequently subjected to treatment in argon or oxygen plasma. The TSEE was observed not only for the plasma treated sheets, but also for the sheets oxidized only, although the intensity of TSEE for the latter was considerably weaker than that for the former with a more negatively charged surface by the plasma treatment. A similar feature was observed for each type of sample : the TSEE activity increased progressively as the SP became more negative and the oxide thickness decreased, being accompanied by the reduction of the oxide and also the deposition of carbon. A mechanism is suggested that the TSEE results from the release of electrons when adsorbed oxygens with a negative charge on the surfaces undergo chemical reduction due to a dehydrogenation of the ethanol, which was used as a quenching gas in the Geiger counter.