Abstract: In a process for producing an aromatic carboxylic acid, it is a dehydrating process which can achieve compactification of a step for removing water from a mixture of acetic acid and water produced in the production process, and which can reduce the consumed energy. In a production process of an aromatic carboxylic acid having an oxidation reaction step for producing a slurry of an aromatic carboxylic acid by carrying out liquid-phase oxidation reaction of an alkyl aromatic compound with an oxygen-containing gas in a solvent containing acetic acid in the presence of an oxidation catalyst, at least a portion of a mixture containing acetic acid and water produced in the production steps is separated into a permeable gas mainly comprising water and nonpermeable substances mainly comprising acetic acid, using a separation membrane having water selectivity.