ZnO and SnO2 thin films were deposited on glass and Polyetherimide (PEI) flexible substrates by spray pyrolysis deposition at low temperature (250 °C). The structural characterization by X-ray diffraction (XRD) reveals that PEI promotes the crystallization of ZnO and SnO2 thin films while the films deposited on glass substrate are amorphous. The physical investigations show that ZnO/PEI and SnO2/PEI have a good crystalline quality and high transparency in visible range (T>80%). Their gap energies are calculated from absorbance data (3.3 eV for ZnO and 3.72 eV for SnO2). Furthermore, the surface properties are investigated by atomic force microscopy and contact angle measurements. It is found that the ZnO/PEI film has a higher surface roughness (RMS = 20.20 nm ± 0.62 nm) compared to SnO2/PEI (RMS = 5.41 nm ± 0.16 nm). The metal oxides (ZnO and SnO2) catalysts exhibit excellent photodegradation activities under UV irradiation up to 80%. The highest activity was observed for ZnO thin films because it exhibits smaller gap energy. Furthermore, both samples show excellent photocatalytic stability.