A process for producing 5-iodo-2-methylbenzoic acid by iodizing 2-methylbenzoic acid, which comprises, as essential steps, a reaction step in which 2-methylbenzoic acid is iodized in the presence of a microporous compound, iodine, an oxidizing agent, and acetic anhydride and a purification step in which sublimation, distillation, crystallization, or a combination of two or more of these is conducted. By the process, 5-iodo-2-methylbenzoic acid, which is useful in functional chemicals such as medicines, can be easily obtained as a high-purity compound in a high yield. The production steps comprising reaction and separation/purification are simple from the standpoint of process operation and the purification load is small. Furthermore, the microporous compound, e.g., a zeolite catalyst, separated and recovered from the liquid resulting from the reaction can be repeatedly used after a simple treatment. Consequently, the catalyst has a long life and the target compound can be produced by the efficient process.