Two kinds of piperidine derivatives including a low-molecular weight (Wt. 481, T770) and a high-molecular weight (Wt. 2000-3100, C944) hindered amine light stabilizers (HALS) are added singly or with ultraviolet absorbers (UVA) in combination to plasticized poly(vinyl chloride) (PVC) samples. Digital photos, color changes, attenuated total refection-Fourier transform infrared spectra (ATR-FTIR), and mechanical properties are obtained to investigate the photostable effect of the light stabilizers on the plasticized PVC after artificial aging. PVC samples with HALS perform well at the first 400 h of irradiation in color change, FTIR, and mechanical properties, but at the last 400 h the photostability decreases. Besides, C944 performs better than T770, because C944 is a high-molecular weight UV stabilizer and has good extraction resistance. Plasticized PVC samples with UVA resist discoloring and photooxidation from the photo-irradiation. Excellent synergism is observed between the combination of HALS and UVA. PVC with HALS/UVA performs better than PVC with HALS and PVC with UVA in color differences, FTIR, and mechanical properties. The synergism is due to the different stages of functions between HALS and UVA. (C) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012