Infrared photodissociation spectra of n-propylbenzene - Ar cluster cations have been observed for the CH stretching vibrational region. Because of very small perturbations due to the Ar cluster formation, the spectra of the cluster cations can be practically regarded as those of the corresponding bare cations. The spectra of the cluster cations were compared with infrared spectra of neutral n-propylbenzene. It was found that substantially spectral changes take place upon ionization not only for the aromatic CH but also for the alkyl CH stretching vibrations. This fact indicates that the positive charge is not localized in the aromatic ring but is penetrated into the propyl side chains.