Abstract: The leaching of cobalt from four-mixed Co-Cu oxidized ores containing cobalt at levels ranging from 0.5wt% to 34wt% was studied and the results has been reported. Conventional dissolution of these oxidized Co-Cu ores with diluted H₂SO₄ and SO₂ as a reducing agent resulted in a substantial improvement in the solution based recovery of cobalt. UV/visible spectroscopic analysis of the leached solutions indicated that the increased cobalt content in the solution was a result of flushing the acidified cobalt leaching solution with SO₂. Furthermore, UV/visible spectroscopy confirmed that as SO₂ was flushed into the acidified leaching solution, Co³⁺ bearing minerals were reduced to the readily soluble Co²⁺ bearing minerals, and this resulted in the increase of total cobalt in the collected solution. The mechanism of the reduction of Co³⁺ to Co²⁺ bearing minerals when SO₂ is flushed during the leaching of mixed Co-Cu oxidized ores, including the stability trends of Co³⁺, Co²⁺, and Cu²⁺ complexes, as shown by their UV/visible spectra, are also discussed.