In the present work, the effects of amount of coke, reduction temperature and furnace types on copper slag smelting in a dc arc furnace were studied. Optimum coke amount was found to be 10% of the slag weight in an open-top furnace for a 1 hour reduction time in the temperature between 1703 K and 1753 K. Similar conditions in a closed-top furnace resulted in higher cobalt and copper contents of the metallic matte, recoveries and reduction rates, as compared with the open-top furnace. In the covered system, for cobalt and copper, recoveries reach 95.7% and 90%, concentrations were 2.38% and 3.51% respectively, and reduction rate constants were found to be 1.7x10(-3).s(-1). For both furnaces, higher reduction temperatures yielded higher reduction rates but lower cobalt, copper and sulfur content in the metallic matte. The specific conductivity of the slag was also estimated by using furnace geometric factor given in the literature as an empirical formula and by using furnace resistance measured during smelting of the copper slag with or without different additives.