Rational　designs　of　the　conductive　layer　below　photocatalytic　films　determine　the　efficiency　of　a　photoanode　for　solar　water　oxidation.　Generally,　transparent　conductive　oxides　(TCOs)　are　widely　used　as　a　conductive　layer.　In　this　mini　review,　the　fundamentals　of　TCOs　are　explained　and　typical　examples　of　nanoscale　TCOs　are　presented　for　application　in　photoelectrochemical　(PEC)　water　oxidation.　In　addition,　hybrid　structures　formed　by　coating　other　photocatalysts　on　nanoscale　TCOs　are　discussed.　In　the　future,　the　nanostructured　electrode　may　inspire　the　design　of　a　series　of　optoelectronic　applications.