The dehydrogenation of ethanol has been studied over a series of Cu/SiO2 catalysts modified with alkaline-earth oxide (Cu-MO/SiO2, M = Mg, Ca, Sr, and Ba). The additive effects of alkaline-earth oxides on copper catalysts were examined by X-ray diffraction, scanning electron microscopy, temperature-programmed reduction, H2-N2O titration, temperature-programmed desorption of CO2, and dehydrogenation of ethanol. The results indicated that the initial turnover frequencies can be improved by adding alkaline-earth oxides into the catalysts. MgO is an excellent promoter for increasing both the activity and stability of Cu/SiO2 catalyst; however, the other alkaline-earth oxide modified catalysts are poor in stability. The increase in turnover frequencies of the modified catalysts is mainly due to the promotional effects of weakly basic sites on Cu metal. The strong basic sites can harm the stabilities of the catalysts.