Redox-type mechanisms of the n-butane oxidative dehydrogenation (ODH), over unpromoted and 3% cesium-promoted nickel molybdate, are clearly put in evidence by a study of the catalyst's electrical conductivity. The in situ data, recorded submitting the catalysts to a sequence of gaseous atmospheres (oxygen-butane-oxygen-reaction mixture), also evidences the n-type semiconductor behavior of the nickel molybdate. The above-mentioned mechanism is also confirmed by temperature-programmed reduction (TPR) and catalytic data. The experiments show that cesium inhibits strongly NiMoO4 reduction under the reaction conditions, keeping the catalyst in a higher oxidation state, Which can be useful for practical applications.