Photoinduced electron transfer between polystyrene and 2,4,6-triphenylpyrylium tetrakis(pentafluorophenyl)gallate (TPPGa) has been studied in dichloromethane solution and in poly(vinyl chloride) film by steady state and time-resolved fluorescence quenching techniques. A dependence of the observed rate constant of fluorescence quenching and the theoretical dependence of the diffusion constant on the molecular weight of the polystyrene were derived. Positive curvature in Stern-Volmer plots for quenching with polystyrene and toluene in solution and negative curvature in the Perrin plot for polystyrene in film was observed. No new absorption or fluorescence bands appeared upon addition of the donor to the dichloromethane solution of TPPGa. Forward and back electron transfer is the possible pathway for stabilization of TPPGa in polystyrene because 100% of TPPGa can be recovered even after prolonged irradiation.