Co/Fe double hydroxides are effective non-precious metal semiconductor compound electrocatalysts for oxygen evolution reaction (OER) in water electrolysis. However, controlled loading of them on rough and conducting substrates is crucial due to their low conductivity. In this work, (CoFe)(OH)(x) nanofilms loaded on coral-like CuO/Cu (CuO/c-Cu) microarray substrates have been prepared in a controllable procedure at an ionic layer level for the first time by successive ionic layer adsorption and reaction (SILAR). The (CoFe)(OH)(x) nanofilm is finely prepared by adjusting the SILAR cycles and the Co/Fe ratio in the precursor solution. The optimized (CoFe)(OH)(x) electrocatalyst demonstrates excellent OER performance with a very low overpotential of 275 mV at 10 mA cm(-2) (with no iR compensation), a small Tafel slope (34 mV dec(-1) with iR compensation), and a long-term durability for at least 10 h in 1 M KOH. We also optimize nanofilms of (CoNi)(OH)(x) and (CoNi)S-x on CuO/cCu by SILAR and achieve satisfactory OER performances. Our results display that fine preparation and optimization of semiconductor nanofilms at an ionic layer level provide a promising strategy on fabrication of high-performance electrocatalysts for OER in water electrolysis.