Calorimetric measurements were carried out on the electrorefining of copper using different current densities with a Calvet type microcalorimeter at room temperature. The ratio (R) of the measured heat (Qm orWm) to the input electric energy (Qin orWin) and the excess heat (Qex orWex), i.e. the difference betweenQm (orWm) andQin (orWin) during the electrorefining process were discussed in terms of general thermodynamics. It was found thatR andQex were related to the current density employed in the experiment and varied as a logarithmic function. The results obtained here indicate that the heat generation under different conditions, such as different currents or voltages, may be caused partially by the irreversibility of the process or by some unknown processes.