The catalytic use of cerium complexes with acetato o-phthaloylbis(1,3-dimethyl-2-pyrazolin-5-one) ligands produced an 88% yield of 3,5-dimethoxy-4-hydroxybenzaldehyde for the oxidation of 3,5-dimethoxycresols by molecular oxygen even in 25% methanolic aqueous solution. The desired compound was obtained up to a 94% yield by increasing the concentration of the substrate or using a 1-propanol aqueous solution. (C) 2002 Elsevier Science B.V. All rights reserved.