To provide a method for efficiently carrying out an acid decomposition while suppressing dehalogenation in an intact state of water solvent because the dehalogenation is caused when the acid decomposition is conducted in the water to lower the yield and a method for removing the water from a phenylhydrazine derivative obtained in an aqueous solution is a process extremely bad at efficiency and a long time is required in the method for carrying out the acid decomposition of the phenylhydrazine derivative and thereby providing phenylhydrazines or mineral acid salts thereof.

This method for producing the phenylhydrazines represented by general formula (2) or mineral acid salts thereof comprises hydrolyzing a phenylhydrazine derivative represented by general formula (1) in the presence of water using a mineral acid in an amount so as to provide ≥6 mol concentration based on 1 kg of water in the reactional system.