The cyclo [18]carbon was very recently determined by experimental observation in condensed phase, it shows quite unusual geometry and electronic characteristics. We have extensively studied its molecular complexes with a wide variety of small molecules. Here we employ sobEDAw to investigate the intermolecular interaction for the open-shell triplet complex O2•• C18, the structure optimized at ωB97XD/def2-TZVP level is shown in Fig. . Because B3LYP-D3(BJ) is found to be completely failed to represent the basic characteristics of cyclo [18]carbon, BHandHLYP is used instead in this instance, we have shown it is adequate to correctly capture the geometry character of this unique system. At BHandHLYP/6-311+G(2d,p) w.CB level, sobEDAw gives ∆Eels = -0.67 kcal/mol, ∆Exrep = 2.97 kcal/mol, ∆Eorb = -0.13 kcal/mol and ∆Edisp = -5.37 kcal/mol, suggesting that only dispersion effect dominates the adsorption of O2 into the ring center of the cyclo [18]carbon. This conclusion is also fully in line with chemical intuition as both O2