In order to obtain insight into the selectivity of Mg2+at the site of bond cleavage of P–O and S–O of the P–O–S linkage, metal ion-promoted alcoholyses of phenyl phosphatosulfate were studied. Mg2+quantitatively promoted P–O bond cleavage in the methanolysis, but mixed cleavage of the P–O bond, which occurred partly due to hydrolysis by trace water and the S–O bond in the reaction of ethanol, 1- or 2-propanol. The ratio of the S–O bond cleavage against the mixed cleavage increased in a order EtOH (11.5%) < n–PrOH (13.3%) < i–PrOH (29.0%). On the other hand, Ca2+and Zn2+promoted selective P–O and S–O bond cleavage, respectively, in the reaction of 2-propanol as well as methanolysis.The medium-dependent change in the selectivity of Mg2+at the site of bond cleavage was discussed.