Systematic theoretical calculations were performed on the interactions between benzene and a variety of MX+ cations (M = Be2+, Mg2+, and Ca2+; X = H-, F-, Cl-, OH-, SH-, CN-, NH2-, and CH3-) in order to expand the scope of the cation-pi interaction. It was found that the basis set and electron correlation effects on the geometry optimization and energy calculation were small. Therefore, the chosen method of this study, MP2/6-311++g(2d,2p)//MP2/6-31+g*, should be sufficiently reliable. Using this method, it was found that the cation-pi interaction between benzene and a naked alkaline earth cation is much stronger than the prototypical benzene-alkali cation interaction. In comparison, when a counterion is introduced into the complex, the C6H6...MX+ interaction is very similar to the benzene-alkali cation in many aspects. Further analyses indicated that electrostatic interaction is the major driving force for C6H6...Li+ and C6H6...Na+ complexes, whereas large charge transfer occurs in C6H6...Be2+ and C6H6...Mg2+ complexes. Electrostatic interaction was also found to be an important driving force for C6H6...MgX+ and C6H6...CaX+. However, electrostatic interaction only accounts for a minor portion of C6H6...BeX+ interaction.