Abstract: Thiiranium heterocycles play an important role in a biocatalytic processes of cells. Usually formation of thiiranium ions are known to proceed by the electrophilic additions of sulfenylhalides to a substituted olefins. We focused attention on the electrophilic addition reaction of methylsulfenyl chloride to the propene. In our work this reaction have been modeled using Ab-initio methods at the MP2/6-31+G(d,f) level of theory to look into the mechanism of the reaction and to explain how the regioselectivity of the reaction is controlled. Calculations of the intrinsic reaction coordinate on the minimum energy pathway revealed the stepwise mechanism for the addition reaction.