This invention relates to the production of penicillamine and acid addition salts of penicillamine through the production from penilloic acid or penicilloic acid formed by hydrolytic decomposition of a penicillin of penicillamine-mercuric-mercaptide which can be easily decomposed by means of hydrogen sulfide to penicillamine. The penicillamine-mercuric-mercaptide is formed as a crystalline precipitate by reaction of the penicilloic acid or penilloic acid with a mercuric salt in a ratio of 1:0.5 in a medium of a water miscible organic solvent and the precipitated penicillamine-mercuric-mercaptide after separation from the reaction medium is decomposed to the penicillamine.