The mechanical response of plasticized thin PVC films under a modulated optical radiation pressure excitation is investigated as a function of the plasticizer content. A resonant behavior with different quality factor depending on the plasticizer content is investigated. The higher the content, the larger the resonant width. A significant thinning of the film is observed, whatever the plasticizer content. The surface tension of the air/solid interface is extracted and shown to hardly vary. The loss factor which is known as the ratio of dissipated energy to stored energy is, on the other hand, dependent on the plasticizer content. In particular, the optical studies reveal that all the energy is always stored at the film interfaces with a dissipation described by the well-known loss factor E\" of the Young’s modulus.