Bioleaching of the copper flue dust emanating from smelters at Sarcheshmeh Copper Complex has been studied. At the present, the dust is sent back to the smelter, which reduces its efficiency. In this study, a continuous system including a feed tank and two-stage aerated stirred tank bioreactors was established. Mixed mesophile bacteria with different amounts of the dust containing 35% of copper mainly in the form of sulfide minerals were used. The effects of pulp densities, residence times and temperatures on the final copper recovery and redox potential were experienced. Despite the copper concentrates bioleaching, the process of dust bio-treating was net acid consuming. Lower pulp densities resulted in a stable redox potential in both reactors. However, increasing the pulp density to 7%, was created an unstable redox potential in the first bioreactor especially at lower temperatures. Final copper recoveries were calculated for pulp densities of 2%, 4% and 7%, were 91.8%, 90.3% and 87.6% with residence times of 2.7, 4 and 6 days respectively. The promising results indicated that bioleaching is a feasible process that can be applied to copper flue dusts.