The rate of extraction of copper from aqueous nitrate media by di(2-ethylhexyl)phosphoric acid (D2EHPA) has been studied both theoretically and experimentally. A kinetic equation involving the diffusional or mass transfer resistance term was developed. The mass transfer resistance was found to have a significant influence on the overall rate of the extraction system. It could be inferred that a second intermediate complex was formed by the reaction of CuR i + with extractant in the organic bulk phase and also that the intrinsic chemical reaction was controlled by this step. A similarity between the Szyszkowski equation and the “interface saturation model” could be observed in the evaluation of the interfacial population of extractant.