A novel non-linear phenomenon, namely simultaneous electrochemical oscillations both on the cathode with Fe(CN)(6)(3)-reduction and on the anode with Fe(CN)(6)(4)-oxidation, is described. Complicated quasi-periodic behavior occurred in the simultaneous potential oscillations by the coupling of the simple period-one oscillations with two incommensurate oscillating frequencies, and complex periodic behavior appeared in the simultaneous current oscillations with the frequency locking.