Several pure and doped alumina samples were characterized by EPR using spin probes and tested in ethanol dehydration. It was found that the concentrations of the electron acceptor sites and the catalytic activity increased when alumina was modified with chlorides and sulfates. Meanwhile, the number of the electron donor sites decreased. A very good correlation between the concentration of the weak acceptor sites and the catalytic activity of the acid-modified catalysts almost passing through the origin of the coordinates was obtained for all the studied samples. Alumina poisoning with sodium resulted in the decrease in the catalytic activity and the concentration of the weak acceptor sites. Therefore, it appears that the weak acceptor sites tested using anthracene are related to the sites active in the ethanol dehydration reaction. (C) 2010 Elsevier Inc. All rights reserved.