Catalytic activity of electrodes towards oxygen evolution reaction was assessed using electrochemically active surface. Paper introduces a new approach using peak current from cyclic voltammetry for the determination of the catalyst surface area with regards to the fractal properties of the electrode using diffusion layer thickness as a scale bar. Three oxide electrode materials: NiCo2O4, Co3O4 and air-oxidized Ni have been prepared by electrodeposition on a nickel substrate (Fig. 1, 4). Cyclic voltammetry in system with Fe3+/Fe2+ red-ox pair (Fig. 2) has been used for active surface area determination. Scaling equation for the determination of fractal dimension and surface area from the dependence of peak current on potential scan rate in a system with red-ox reaction has been derived (Fig. 3, 5). The surface of the electrode with nickel cobaltite layer demonstrated fractal properties with fractal dimension of 2.33 ± 0.15 (Fig. 5). Electrochemically active surface of fractal NiCo2O4 increased by 60% when scan rate was changing from 20 to 500 mV/s, while Ni and Co3O4 active surface remained constant at 1,07±0,07 and 1,67 ± 0,10 cm2 respectively (Table 1). Voltamperograms at different scan rates recalculated for current density using active surface areas are similar (Fig.6) for different electrodes. Maijor factor affecting NiCo2O4 performance towards oxygen evolution is more extensive factor, than its catalytic activity.