A process for allowing an oxidation reaction efficiently to produce an object aromatic carboxylic acid with an efficient productivity by improving a catalyst activity even in the presence of a relatively small amount of a catalyst is provided.The process comprises oxygen-oxidizing an aromatic compound having an alkyl group and/or an alkylene group as a substrate in the presence of a catalyst containing a cyclic imino unit having an N—OR group (wherein R represents a hydrogen atom or a protecting group for a hydroxyl group) and a transition metal co-catalyst (a cobalt compound, a manganese compound, and a zirconium compound) to produce the aromatic carboxylic acid corresponding to the aromatic compound. The oxidation reaction is carried out with feeding a mixture of the catalyst and at least one member selected from the group consisting of the substrate, a reaction intermediate (e.g., a ketone and an aldehyde), and a reaction product (e.g., water and an aromatic carboxylic acid) successively or continuously to the oxidation reaction system. The oxidation reaction may usually be carried out in the absence of a reaction solvent. The reaction may be conducted with removing water produced by the reaction from the reaction system.