Two series of the compounded polypropylene(PP)containing 0.5 wt% of the photo initiators, PIs, (four aromatic carbonyl and, two ferric compounds) with and without 6 wt% corn starch were processed in a torque rheometer at 180 °C for 5 min in a closed system. The uniform compression molded films (0.15 mm thick) were solar radiated in the natural weathering conditions during a summer days. The aim of this work is to show susceptibility of these compounds to natural weathering conditions. The solar radiation effects on chemical changes of the film samples were studied using a FTIR and UV spectrophotometers. The results show that the PP-PI and PP-starch-PI samples are much more susceptible to degradation than pure PP. The presence of Starch and PI in the PP increase the formation of carbonyl group as a result of chain scission. Ferric stearate and Irgacure184 among the PIs in the PP with and without starch show the highest and lowest susceptibility, respectively. Carbonyl formation of the films (measured by FTIR) shows a linear increase followed by higher rate after 5 days of solar radiation. UV absorption spectra of the films show a significant reduction (in the range of 235–270 nm) during first 2 days of sunlight exposure. Also, embrittlement time of the samples was reduced by increase in the radiation time.