A novel photodegradable TiO2-Fe(St)3-polystyrene (TiO2-Fe(St)3-PS) nanocomposite was prepared by embedding TiO2 and Fe(St)3 into the commercial polystyrene. Ferric stearate was added into polymer as cocatalyst in order to improve the dispersion in polystyrene and photocatalytic efficiency of TiO2 nanoparticles. Solid-phase photocatalytic degradation of the TiO2-Fe(St)3-PS nanocomposite was carried out in an ambient air at room temperature under ultraviolet lamp. The properties of TiO2-Fe(St)3-PS composite film were compared with that of the pure PS film and the TiO2-PS composite film, through weight loss monitoring, scanning electron microscope, gel permeation chromatogram, and FTIR spectroscopy. The photodegradation efficiency of TiO2-Fe(St)3-PS composite film was higher than that of the pure PS film and the TiO2-PS composite film under the UV light irradiation. The average molecular weight (Mw) of TiO2-Fe(St)3-PS composite film decreased 63.08%, and the number of average molecular weight (Mn) decreased 79.49% after UV light irradiation for 480 h. Photo-oxidation leads to an increase in the low molecular weight fraction by chain scission, thereby facilitating biodegradation. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013