Abstract The electronic spectrum of the mono-positive ions of perylene formed by the interaction of antimony pentachloride was examined in various solvents. The observed spectra may be classified into two types. The one is the spectrum observed when the solvent is of a high dielectric constant, a spectrum which almost coincides with the spectrum of perylene in sulfuric acid. The other is the spectrum observed for a solution in a solvent of a low dielectric constant, a spectrum consisting of broad absorption bands accompanied by an extra band at about 1200 mμ. The former type of spectrum may be attributed to the perylene ions in a free state stabilized by the solvation, and the latter to an associated state involving perylene and antimony pentachloride ions. It is suggested that, in the association of both kinds of ions, two or more perylene ions are in contact with each other, and that the interaction between them is responsible for the shift and broadening of the absorption bands of perylene ions, as well as for the appearance of the extra band.