B3LYP/6-31G(d,p) method was used to study proton transfer in CF 3 SO 3 H⋯(H 2 O) n , CF 3 SO 3 H⋯(C 3 N 2 H 4 ) n (imidazole) and CF 3 SO 3 H⋯(C 3 N 2 H 4 ) n (pyrazole) clusters. Structural parameters, proton affinities and vibrational frequencies were calculated in this study. Our calculations were in good agreement with the available experimental values. The ν(OH) stretching frequency of CF 3 SO 3 H⋯(H 2 O) n clusters changes from 3749cm −1 for n=0, to 2908cm −1 for n=1 and 2239cm −1 for n=2, showing its strong red-shift when the first and the second water molecules are attached. It was found that n c =3 is the critical size for the intermolecular proton transfer in CF 3 SO 3 H⋯(H 2 O) n clusters, n c =1 in both CF 3 SO 3 H⋯(C 3 N 2 H 4 ) n (imidazole) and CF 3 SO 3 H⋯(C 3 N 2 H 4 ) n (pyrazole) clusters. The order of their proton affinities is as follows: imidazole (10.37)>pyrazole (9.83)>water (7.73), indicating that the proton is more easily transferred in CF 3 SO 3 H⋯(C 3 N 2 H 4 ) n (imidazole) clusters than in CF 3 SO 3 H⋯(H 2 O) n and CF 3 SO 3 H⋯(C 3 N 2 H 4 ) n (pyrazole) clusters.