The alcoholysis of 1,2-thiazetidine 1,1-dioxide has been investigated using ab initio and density functional theory at HF/6-31G*, MP2/6-31G*//HF/6-31G* and B3LYP/6-31G* levels. The geometries, energies and frequencies of all stationary points were calculated in detail. Solvent effects have been considered by means of a polarizable continuum model (PCM). Our results indicate the lcoholysis of 1,2-thiazetidine 1,1-dioxide proceeds via concerted mechanism and stepwise mechanism. In the stepwise mechanism, two possible reaction pathways can be followed whilst one possible reaction pathway can be followed in the concerted mechanism. The most favorite pathway for lcoholysis of 1,2-thiazetidine 1,1-dioxide was found.