To provide a method for efficiently oxidizing a substituent group of a substituted aromatic compound having oxidizable substituent groups, e.g. 4,4'-dialkylbiphenyl.

Oxidation reaction of the substituted aromatic compound is carried out in the presence of a resin base having a pyridine base by using a solvent composed of a nonaromatic compound having one or more tertiary carbon atoms, e.g. isobutane or methylcyclohexane. Air is preferably used as an oxidizing agent.