The self induced diastereoselective oxidation of several thio-β-d-galactopyranosides to the corresponding sulfoxides, has been shown to occur in high yield. Up to 74% diastereomeric excess could be obtained depending on the structure and the conformation of the starting thioglycoside. Rs and Ss Phenylsulfinyl-β-d-galactopyranosides have been obtained in optically pure forms, their chemical as well