Flame-retardant polyvinylchloride (FRPVC), typically used in cable insulation and jacketing construction for multi-purpose reactor (MPR) at Atomic Energy Authority of as well as carbon-black FRPVC (CB-FRPVC) and nonflame-retardant PVC and CB-PVC materials produced by Egyptian Electrical Cable Company (EECC), have been irradiated up to 160 KGy, at room temperature with a Co-60 gamma source. Free-volumes and thermal stability of irradiated and nonirradiated PVC samples have been examined using positron annihilation Lifetime Spectroscopy (PALS) and thermogravimetric analysis (TGA). In addition, the mechanical properties: tensile strength and elongation at break were examined. Considerable presence of flame-retardant and carbon black additives in CB-FRPVC sample led to both quenching and inhibition of Ps formation. The mechanical and thermal Characterization showed that irradiation of PVC samples up to 80 KGy effectively induced cross-linking to maxima. Higher doses then after results in degradation and thus a decrease in mechanical strength. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 199-206, 2009