In the presence of a catalytic amount of cesium hydroxide,the corresponding S-aryl phosphorothioates can be obtained by the reactions of dialkyl phosphites with diaryldisulfdes in excellent yields at room temperature,using DMSO as a solvent.The reaction mechanism was discussed.The method provides a new and expedient path for the preparation of S-aryl phosphorothioates. The presence of a catalytic amount of cesium hydroxide, the corresponding S-aryl phosphorothioates can be obtained by the reactions of dialkyl phosphites with diaryldisulfdes in excellent yields at room temperature, using DMSO as a solvent. The reaction mechanism was discussed. a new and expedient path for the preparation of S-aryl phosphorothioates.