A transient natural convection develops along vertical plane Cu electrodes during modulation of the electrolytic current in the copper refining process. The electrolysis modes of "Current On," "Current Off," and "Current Reverse" are frequently encountered in industrial electrolysis. The time variation of both the concentration profile of Cu2+ ion and the velocity profile in a 0.6 M CuSO4 aqueous electrolyte confined between both vertical electrodes had been reported in a laboratory-scale electrolytic cell. The mass transfer rate of Cu2+ ion as well as the natural convective fluid motion is now numerically analyzed under the presumption of uniform current density distribution along electrode height. Calculated transient concentration and velocity profiles accompanied with various switching modes of the electrolytic process quantitatively agree well with the measurements. (C) 2008 The Electrochemical Society.