The charge transfer process C + (2s 2 2p) 2 P+S(3s 2 3p 4 ) 3 P→C(2s 2 2p 2 ) 3 P+S + (3s 2 3p 3 ) 4 S is important in the modellisation of the interstellar medium chemistry. The rate constant generally used in the astrochemical models for the C + +S→C+S + reaction is 1.5×10 −9 cm 3 s −1 [1] between 10K and 41000K, but it remains uncertain for such a large domain of temperature. Since no precise calculation has been ever performed for this process, we have undertaken the first complete ab initio molecular treatment of this collision, followed by a semi-classical dynamics. The results suggest that the rate constant adopted in astrochemical models might be overestimated.