Nanoporous Co 3 O 4 (po-Co 3 O 4 ) films have been prepared on stainless steel substrate by a novel two-step method. Firstly, a composite Co 3 O 4 -SiO 2 film was fabricated via electrochemical co-deposition under a cathodic potential from the mixed sol-gel precursor. Then, the obtained composite film was underwent consecutive cycling voltammetries in a concentrated KOH solution to etch the SiO 2 component, leading to the formation of po-Co 3 O 4 films. The resultant film electrode exhibits satisfactory electrocatalytic property towards the oxygen evolution reaction (OER).