The key for successful and efficient dissolution of copper, nickel and cobalt from ocean nodules depends on prior reduction of the manganese and ferric oxides with which the above valuable nonferrous metals are interlocked. We have shown that through the application of negative reduction potential or DC current, significant reduction of manganic and iron oxides in the ocean nodules can be achieved, thus liberating the occluded copper, nickel and cobalt for easy dissolution in an acid medium. Polarization studies using a slurry electrode system indicated that maximum dissolution of iron and manganese due to electrochemical reduction occurred at negative DC potentials of -600mV(SCE) and -1400mV(SCE). Electroleaching of the ocean nodules at the above negative applied DC potentials resulted in significant dissolution of copper, nickel and cobalt in IM H2SO4.