This Bureau of Mines report discusses research involving the leaching of low-grade molybdenum-bearing copper ore. The molybdenum concentration found in sulfuric acid leachate from low-grade copper ores is typically less than 2 ppm. Research was performed to determine conditions required to improve molybdenum solubilization. The variables studied were ph, oxidation-reduction potential, metal ion concentrations, and nature of oxidant type. In both basic and acidic (stirred) reactor tests, over 80 pct of the molybdenum was extracted at ambient temperature and pressure in 24 h (or less) with strong oxidizing reagents such as naclo in a basic medium or in an hno3-hcl solution. With weaker oxidants, such as h2o2 and mNO2 in h2so4 solution at ph 1, <2 pct of the molybdenum was extracted. With basic solutions and lean ore (0.03 pct mo), 210 times stoichiometric of naclo was required to obtain 80 pct extraction in 24 h. The extractions at ph <1 or near 10 were dependent on the oxidizing power of the oxidant rather than the solubility limit of molybdenum. However, at about ph3, the presence of 0.1 to 0.3 G/l ferric ions precipitated >80 pct of the molybdenum from a prepared solution while other metal ions common to dump leach liquor, such as cu2+, mn2+, mg2+, and al3+ removed <20 pct of the molybdenum. Therefore, in order to obtain high (80 pct) molybdenum extractions from copper ores, the ph of the leach must be <0.5 Or approximately 10, and the initial oxidation-reduction potential of the lixiviant must be >0.8 V for acidic leaching.