The property changes of polymeric films upon degradation are important to develop strategies to prolong the device lifetimes. In this regard, we investigated the effects of ultraviolet-ozone (UVO) treatment on the electronic structures of poly (9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) and poly (9,9-di-n-octylfluorenyl-2,7-diyl) (PFO) films. We found that as the UVO treatment time increased, the intensities of the UV-vis and photoluminescence spectra of both F8BT and PFO films exponentially decayed owing to the destruction of the conjugated system of the films. As per the X-ray photoelectron spectra, both the F8BT and PFO films showed significant oxidation and p-doping effects upon UVO treatment. In addition, UVO treatment caused the etching of the polymeric films, and their thickness gradually decreased; the etching rate with UVO treatment was faster for PFO than for F8BT. These results indicate that the functionalization of polymers with UVO treatment requires the careful consideration of the resulting changes in their electronic structure.