The electrochemical behaviors of a copper electrode in alkaline solutions containing NaHCO3 and Na2CO3 have been in-situ studied by using an electrochemical quartz crystal microbalance (EQCM) combined with cyclic voltammetry (CV) technique. Through the voltammetry and mass curves recorded simultaneously, the effective equivalent molar mass (EMM) as a function of the potential was obtained and applied to identification of the reaction species of the electro-formed and electro-induced layers. As for a copper in 0.05 M NaHCO3 + 0.05 M Na2CO3 solution, the electrode reaction mechanisms were proposed on the basis of the analysis of EQCM data. The results indicated that the initial formations of the anodic layer involve an inner Cu2O layer, followed by a middle CuO-Cu(OH)(2) layer, and finally a complex outer [Cu(OH)(2). CuCO3] layer with two possible formula. It was detected that the formation of soluble Cu(TI) species in the anodic scan and the re-formed precipitation of these soluble species in the cathodic scan, accompanying a decrease and an increase of the electrode mass, respectively. The latter was found to be effectively hindered by the two cathodic reduction reactions. The difference of EQCM responses From a copper in solutions containing different NaHCO3-Na2CO3 concentration ratios was discussed according to the electrode reaction mechanisms proposed.