Sulfite may be added to copper cyanide solutions to reduce cyanide oxidation at the anode during copper electrowinning. Anodic sulfite oxidation is enhanced in the presence of copper cyanide. Sulfite also suppresses the oxidation of copper cyanide. The effect of sulfite on the oxidation of copper cyanide decreases with increasing mole ratio of cyanide to copper. This is related to the shift in the discharged species from Cu(CN)(3)(2-) to Cu(CN)(4)(3-) with increasing mole ratio of cyanide to copper. Sulfite is oxidized to sulfate. At [Cu+] = around 1 M, CN: Cu = 3.0-3.2, [OH-] = 0.05-0.25 M, [SO32-] = 0.4-0.6 M and the temperature = 50-60 degreesC, the anodic current efficiency of sulfite reached 80-90%. With further increase in sulfite concentration beyond 0.6 M, the current efficiency of sulfite oxidation will not be increased significantly. Further increase in CN:Cu mole ratio will result in decrease in the anodic current efficiency.