In this paper, photorefractive effect in a doped polymer system with a low glasstransition temperature (Tg) is reported. Photoconductivity of a PVK-C60 thin film has beeninvestigated and electro-optic coefficiency of a PVK-nitroazobenzene thin film has beenmeasured. Optical degenerate four-wave mixing and two-beam coupling experiments havebeen done in the thick film of PVK-C60-nitroazabenzene-dibutyl phthalate (DBP). Thediffraction efficiency of 1. 5% for the four-wave mixing was obtained under a relatively low field of 16.4 V/μm. The experimental results reveal that the plasticizer, DBP, effectively enhanced the photorefrective effect by an orientational mechanism, and the property of the photorefractivity of the material has been improved.