A mix-valenced nickel oxide, NiOx, was prepared from nickel nitrate aqueous solution through a precipitation with sodium hydroxide and an oxidation by sodium hypochlorite. Further, pure nickel oxide was obtained from the NiOx, by calcination at 300, 400 and 500 degrees C (labeled as C300, C400 and C500, respectively). They were characterized by thermogravimetry (TG), X-ray diffraction (XRD), nitrogen adsorption at -196 degrees C and temperature-programmed reduction (TPR). Their catalytic activities towards the degradation of phenol were further studied under continuous bubbling of air through the liquid phase. Also, the effects of pH, temperature and kinds of nickel oxide on the efficiency of the microwave-enhance catalytic degradation (MECD) of phenol have been investigated. The results indicated that the relative activity affected significantly with the oxidation state of nickel, surface area and surface acidity of nickel oxide, i.e., NiOx, (>+2 and S-BET = 201 m(2) g(-1)) C300 (+2 and S-BET = 104 m(2) g(-1)) > C400 (+2 and S-BET = 52 m(2) g(-1)) > C500 (+2 and S-BET = 27 m(2) g-(1)). The introduction of microwave irradiation could greatly shorten the time of phenol degradation. (c) 2006 Elsevier B.V. All rights reserved.