Calculations on alkaline earth metal ion-benzene complexes were performed using the density-functional theory (DFT) B3LYP and ab initio MP2 methods. They showed that the interaction is very strong, of the order of magnitude of a normal chemical bond. Electrostatic interaction is not the dominant component, and both charge transfer and induction make a significant contribution. Analysis of molecular orbital interactions indicated that binding of the alkaline earth metal ions to benzene may be attributed to s-pi and p-pi interactions, which are significantly stronger than those between alkali cations and benzene.