The mechanism and the kinetics of the reaction between HS and Cl-2 leading to HSCl and Cl were studied theoretically. The effect of the complete basis set limit (CBS) was included by extrapolating the results obtained with cc-pVDZ, cc-pVTZ and cc-pVQZ correlation consistent basis sets functions. At the highest level of calculation CCSD(T), the calculated rate constant is 1.0 x 10(-12) cm(3) molecule(-1) s(-1). The activation Gibbs free energy was calculated to be 7.4 kcal/mol, which is only 0.2 kcal/mol above the value determined experimentally. The enthalpy and Gibbs free energies of the reaction are - 6.9 and - 6.5 kcal/mol, respectively.