The effect Of CO2 in promoting the aerial oxidation of para-methyl anisole (PMA) to para-methoxy benzaldehyde (PMB) and anisic acid (AnA) over the Co/Mn catalyst system in acetic acid medium has been investigated. Significant enhancement of catalytic activity and selectivity toward PMB and AnA in the presence Of CO2 is observed at the reaction temperature of 393 K. UV-visible investigations of the catalyst system reveal that the formation of Co(III) species is enhanced by the help of CO2, which is probably associated with the CO2 promotional effect. (C) 2003 Elsevier Science B.V. All rights reserved.