A process for producing aziridine-2-carboxylic acid or its salts is provided which comprises treating an alphahalogeno-beta-aminopropionitrile or its mineral acid salt with an alkali or alkaline earth metal hydroxide in water or in a water-containing organic solvent. In a preferred embodiment, aziridine-2-carboxylic acid or its salt is produced by treating the reaction mixture containing an alpha-halogenobeta-aminopropionitrile obtained by reacting an alpha, beta-dihalogenopropionitrile or an alpha-halogenoacrylonitrile with ammonia, with an alkali or alkaline earth metal hydroxide in the presence of water without isolating the alpha-halogeno-beta-aminopropionitrile from the reaction mixture beforehand.
