This study is an attempt to investigate the effect of a representative pro-oxidant (manganese stearate) on the degradation behavior of 70 +/-5 mu thickness films of LDPE, LLDPE and their blends. Films were prepared by film blowing technique in the presence of varying quantities of manganese stearate (0.5-1% w/w) and subsequently subjected to accelerated degradative tests: xenon arc exposure and air-oven exposure (at 70 degrees C). The physico-chemical changes induced as a result of aging were followed by monitoring the mechanical properties (Tensile strength and Elongation at break), carbonyl index (Cl), morphology (SEM), melt flow index (MFI), oxygen content (Elemental analysis), and DSC crystallinity. The results indicate that the degradative effect of pro-oxidant is more pronounced in LDPE than LLDPE and blends, due to the presence of larger number of weak branches in the former. The degradation was also found to be proportional to the concentration of the pro-oxidant. Flynn-Wall-Ozawa iso-conversion technique was used to determine the kinetic parameters of degradation, which were used to determine the effect of the pro-oxidant on the theoretical lifetime of the polymer. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 524-533, 2010