Abstract The electronic absorption spectra of pure Langmuir (L) films of 6MeDS prepared upon MgCl2, CaCl2, CdCl2, and CuCl2 aqueous solutions have shown that the Mg2+, Ca2+, and Cd2+ cations promote the J-aggregation of the dye, but the Cu2+ cation inhibits it. Instead, the Cu2+ cation promotes the formation of another type of dye aggregate (D-aggregate), which exhibits a split electronic absorption band. These L films have been transferred onto solid substrates by the Langmuir–Blodgett (LB) technique. The vibronic absorption spectra observed for the obtained LB films have shown the similarity between the metal–cation-containing J-aggregate and the metal-free J-aggregate of the dye, the latter of which was characterized in the previous study [K. Ikegami, J. Chem. Phys. 121 (2004) 2337]. These spectra have also indicated that the bimolecular metal chelation plays an important role in the J-aggregation, like the intermolecular hydrogen bonding in the metal-free case.