Abstract The addition of 1-thio- d-glucose sodium salt to per- O-acetylated 1,2-dideoxy-1-nitro- d- arabino-hex-1-enitol, readily available from d-arabinose, afforded the corresponding 2- S-glycosylated 1-deoxy-1-nitro- d-mannitol and - d-glucitol peracetates. These, after deacetylation, were transformed by the Nef reaction to 2-thioepisophorose and 2-thiosophorose, respectively. The 2-thiodisaccharides easily epimerize in aqueous sodium bicarbonate at ambient temperature to a 1:4 equilibrium mixture. The predominant 2-thiosophorose was obtained crystalline. A 1H NMR study of the epimerization in deuterium oxide showed that the reaction involves an H-2 proton exchange mechanism.