Abstract: α,α'-Dimercapto-succinic acid was prepared by a simple synthesis involving the addition of thioacetic acid to the disodium salt of acetylene dicarboxylic acid (tetrahydrate), in the presence of dilute sulphuric acid (36.2%) and with pyridine as catalyst, followed by hydrolysis of the resulting addition compound. The disodium salt of acetylene dicarboxylic acid (tetrahydrate) was obtained from dibromosuccinic acid by treating the latter with an excess of concentrated sodium hydroxide solution.