A molecular interaction between a methane/fluoromethane molecule and a benzene/hexafluorobenzene molecule was theoretically studied. Attractive interaction between the fluorine atom of the fluoromethane and the T-system of the hexafluorobenzene was observed (C-F/pi(F) interaction, -2.43 kcal/mol in MP2/aug-cc-pVDZ). The attractive C-F/pi(F) interaction energy was larger than that of the interaction between methane and benzene (C - H/pi(H) interaction, - 1.47kcal/mol). On the other hand, the very weak repulsive interaction was observed between the fluorine atom of the fluoromethane and the benzene (C-F/pi(H) interaction, +0.12 kcal/mol). The interaction energies between methane and benzene (C-H/pi(H) interaction, -1.47 kcal/mol) and between methane and hexafluorobenzene (C-H/pi(F) interaction, -1.36 kcal/mol) were almost the same.