Photodegradation of PLA/PE, PLA/PE/TiO2 nanospheres and PLA/PE/TiO2 nanotubes was obtained under simulated sunlight. The nanocomposites were analyzed by infrared spectroscopy, scanning electron microscopy and tensile-deformation measurements. TiO2 nanospheres and TiO2 nanotubes were found to present different effects on the crystallinity of PLA and a straight correlation between structural organization and photostability was observed. According to the results, TiO2 promotes the degradation of PLA and PE, affecting the organizational level of the polymers. By adding TiO2 nanoparticles to the PLA/PE films, vibration modes characteristic of degradation products were promptly observed and the lifetime of the polymer decreased when compared to the PLA/PE without TiO2 nanoparticles. Mechanical measurements showed an improvement of the mechanical properties when adding the TiO2 nanoparticles.