The processes occurring at NiO and CoO monocrystalline electrodes in a basic Li + Na carbonate melt have been investigated at 923 K by electrochemical impedance spectroscopy (EIS). Four various equivalent circuits (two for the NiO electrode and two for the CoO electrode) were employed to examine the data obtained. These equivalent circuits consist of elements that represent the reduction-oxidation of oxygen entities dissolved in the melt, incorporation-extraction of Li+ ions into/from the crystallographic network of either Ni or Co oxides and semicondutance properties of electrode materials, The effect of time elapsing since the electrode immersion on the behaviours of these elements was analysed to verify a reliability of the applied models.