Photodegradation of plasticized poly(vinyl chloride) (PVC) stabilized by different thermal stabilizers including organic calcium complex and mercaptide organotin was investigated. Plasticized PVC sheets prepared by an open twin-roller mill and plate vulcanizing machine were exposed to xenon-arc light with the irradiance of 0.51 W/(m(2).nm) at 65 degrees C. A much better color stability displayed by mercaptide organotin than organic calcium complex has been confirmed by digital photos and color difference. This can be explained that the more effective mercaptide organotin minimizes the amount of thermal damage from processing thus favours subsequent UV weathering. Carbonyl index and decomposition activation energy (E-a1) obtained from attenuated total refection-Fourier transform infrared spectra (ATR-FTIR) and thermogravimetric (TG) analysis, respectively, further indicate that plasticized PVC sheets containing mercaptide organotin have more excellent UV resistance. Mechanical tests reveal that photodegradation of PVC is accompanied by the predominant process of chain scission on the surface of samples. POLYM. ENG. SCI., 51:624-631, 2011. (C) 2010 Society of Plastics Engineers