The anisotropy of current-induced density (ACID) is an intuitive and universally applicable method for visual analysis of electron delocalization by generating molecular ring current induced under a given external magnetic field , which can be further decomposed into the contributions of different types of molecular orbitals to gain a deeper insight. The ACID isosurfaces of π out and π in electrons, respectively referred to as ACID- out and ACID- in , in C 18 -(CO) n (n = 6, 4, and 2) are plotted in Fig. . It can be seen that the π out electrons of all three precursors show complete and obvious diatropic ring currents, which conform to the left-hand rule with the direction of the external magnetic field. The unidirectional ring currents caused by π out electrons are basically distributed at the region above/below the ring. This observation provides strong evidence for the out-of-plane aromaticity of the C 18 -(CO) n (n = 6, 4, and 2). Furthermore, the ACID- out isosurface of the precursors widens and the ring current density increases with the decrease of number of -CO groups in the molecule, indicating that the molecular aromaticity created by π out electrons gradually strengthens in the order of C 18 -(CO) 6 < C 18 -(CO) 4 < C 18 -(CO) 2 . The ACID isosurface of the π in electron system, namely ACID- in , in the molecules shows the truncation of the in-plane ring current near the -CO groups. In particular, the increase of the number of -CO groups results in an enhanced hindrance of global ring current and leads to more appearance of multidirectional local induced currents.