The　amount　of　active　sites　of　a　catalyst　is　of　great　importance　to　enhance　the　oxygen　evolution　reaction　(OER)　activity.　Here,　the　sheet-on-sheet　strategy　is　proposed　to　effectively　increase　the　density　of　active　sites　of　NiFe　layered　double　hydroxide　(NiFe　LDH)　catalyst　in　terms　of　structural　engineering.　As　a　non-precious　electrocatalyst　for　the　OER,　NiFe　LDH　is　grown　directly　on　CuO　nanosheets.　As　a　result,　the　received　NiFe　LDH/CuO　nanosheet　catalyst　with　sheet-on-sheet　structure　shows　an　ultralow　overpotential　of　270　mV　at　20　mA　cm-2,　much　lower　than　that　of　RuO2　as　a　benchmark.　The　CuO　nanosheets,　as　substrate,　play　the　vital　role　in　downsizing　the　NiFe　LDH,　leading　to　the　raised　active　site　density.　©　The　Royal　Society　of　Chemistry.