Poly(vinyl alcohol)/poly(ethylene glycol) (PVA/PEG) copolymer was prepared using casting technique. The obtained PVA/PEG thin films have been irradiated with gamma rays with doses ranging from 1.5 to 20 Gy. The resultant effect of gamma irradiation on the thermal properties of PVA/PEG has been investigated using thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The onset temperature of decomposition T o and activation energy of thermal decomposition E a were calculated, results indicating that the PVA/PEG thin film decomposes in one main weight loss stage. Also, the gamma irradiation in dose range 4-12 Gy led to a more compact structure of PVA/PEG copolymer, which resulted in an improvement in its thermal stability with an increase in the activation energy of thermal decomposition. The variation of transition temperatures with gamma dose has been determined using DTA. The PVA/PEG thermograms were characterized by the appearance of an endothermic peak due to melting of crystalline phase. In addition, structural property studies using X-ray diffraction and infrared spectroscopy were performed on both nonirradiated and irradiated samples. Furthermore, the transmission of the PVA/ PEG samples and any color changes were studied. The color intensity (E was greatly increased with increasing the gamma dose and was accompanied by a significant increase in the blue and green color components. V C 2011 Wiley Periodicals, Inc. J Appl Polym Sci 124: [654][655][656][657][658][659][660] 2012