The reactions between S-nitrosothiols and phosphite esters, including P(OPh)3, P(OBn)3, and P(OEt)3, were studied. Two different conjugated adducts, thiophosphoramidates and phosphorothioates, were formed, depending on the structures of the S-nitrosothiol substrate (e.g., primary vs tertiary). These reactions proceeded under mild conditions, and the reaction mechanisms were studied using experiments and calculations.