This study prepares PdO nanostructures on a SiO2 substrate by reactive-sputter deposition and examines photoresponse characteristics of the thin films. PdO thin films deposited at 25 °C is composed of bowed nanoflakes standing on the SiO2 substrate, which have a single-crystalline structure after thermal anneal at 400 °C. The 400 °C -annealed nanoflake thin film has a band gap energy in the red-light range (∼2.06 eV), and exhibits a very sensitive photoresponse upon the UV (365 nm) illumination. The high photoresponse sensitivity of the 400 °C -annealed nanoflake thin film is ascribed to a lower density of recombination centers and traps due to an excellent crystallinity and a high carrier extraction efficiency due to a low electrical resistivity. A slight decrease in the photocurrent density during the initial stage of the UV illumination is attributed to adsorption of O2- anions on the 400 °C -annealed nanoflakes.