This study aims at modifying ceramic membranes by means of alcohol chemisorption. Composite ceramic membranes with a skin layer of gamma -alumina were used. First, the adsorption of several alcohol on powdered gamma -alumina was investigated emphasising the thermal stability of the adsorbed compounds. Later, a commercial gamma -alumina membrane was modified by alcohol adsorption. The permeability of water and several organic compounds was obtained for both the non-modified and modified ceramic membrane. Also, its isoelectric point was determined. The results prove that all the alcohol were readily adsorbed on powdered gamma -alumina not only physically but also chemically forming an alkoxide. The chemisorbed alcohol was stable up to 200 degreesC. Beyond this temperature, the alkoxide breaks up releasing the alcohol although the alkoxide also can react yielding an olefin or ether. The ceramic membrane was also successfully modified by alcohol adsorption. The layer of chemisorbed alcohol imparts hydrophobic characteristics to the membrane surface, so water permeability decreases significantly. This cannot be merely explained by pore size reduction due to the adsorbed layer. Thermal treatment at 250 degreesC recovered original permeability with only minor damage to the membrane.