Reported herein is a stereoselective route to anti-β-hydroxy sulfoxides via the reaction of epoxides and sulfenate anions. Extensive experimental/computational studies revealed the dual special roles of MgBr2·OEt2, serving to generate the bromohydrin alkoxide intermediate, which undergoes nucleophilic attack of the prochiral sulfenate in a diastereoselective manner. The present study has opened a general, stereoselective synthetic route to anti-β-hydroxy sulfoxides.