To obtain a carboxylic acid without producing by-products such as ammonium hydrogensulfite.

This method for producing carboxylic acid comprises (1) a carboxylic acid salt-producing process comprising (a) producing at least corresponding amide, hydrolyzing the resultant amide in the presence of a base and producing the corresponding carboxylic acid salt or (b) producing at least corresponding carboxylic acid salt by reacting a microorganism having ability to hydrate a nitrile such as cyanhydrin compound or its treated material with the nitrile and (2) electrodialysis process for subjecting the carboxylic acid salt produced in the carboxylic acid salt-producing process to electrodialysis and producing the corresponding carboxylic acid and a base. A microorganism belonging to the genus Pantoea or Gordona is contained in the microorganism having ability to hydrate nitrile. Ammonia produced in the carboxylic acid salt-producing process (1) can be utilized as a nitrogen source in production process of nitrile.