This study investigated the influence of UV-radiation on structural and uniaxial tensile properties of tannic acid (TA)/polyvinyl alcohol (PVA) composite films. All the samples were exposed to UV light. It was observed that TA reinforced the structure of PVA and its uniaxial tensile properties, as TA concentration increased thanks to the formation of crosslinking between TA and PVA molecules. From X-ray diffraction (XRD) measurements, it was seen that TA had a better protective effect on ordered structures such as crystallites against UV irradiation than that of PVA films, because the crystallinity of TA/PVA films did not change much. Major degradation effect of UV-radiation was seen on the amorphous flexible PVA chains and structure. As a result of photodegradation process leading to possibly breakage in the polymer chains in especially amorphous structure, the extensibility or strain at break values of both pure PVA and TA/PVA composite films was decreased dramatically. However, because decrease in the strain at break values for 5% and 10% TA content is less than that for 15% and 20% TA content, the 5% and 10% TA content can be regarded as optimum values, when the protective role of TA against UV irradiation was considered in the studied films.