Ru-modified alumina composite membranes were prepared by the sol-gel method. The pore size distribution from nitrogen adsorption showed that average pore diameters were 3.1-4.5 nm, and the ideal separation factor was obviously higher than that of a pure gamma-Al2O3 membrane. Ethanol dehydrogenation was carried out in the Ru-modified alumina membrane reactors. The effects of the reaction temperature, feed rate, and argon sweep flow rate on acetaldehyde yield were investigated. The results showed that the yield of acetaldehyde increased by 25-28% at the same conditions in a Ru-modified alumina membrane reactor. The reduced temperature of the Ru-modified alumina composite membrane was measured by temperature-programmed reduction, and the morphology of the membrane was characterized by SEM, TEM, and XRD.