The complexes formed by cyclooctatetraene (COT) and alkaline earth metals were theoretically studied but without convincible experimental evidence. To validate very strong cation-pi interaction in the complexes, the NMR properties are experimentally recorded and theoretically calculated in this study. The good agreement between the recorded C-13 NMR data and all the calculated results, including NMR chemical shift, interaction distances and strength, and atomic charge in DMSO at different theoretical levels by PCM method, strongly indicates that the complexes between COT and alkaline earth metal atoms do exist via strong cation-p interaction. (C) 2008 Elsevier B. V. All rights reserved.