The effect of a water-immiscible organic acid on the kinetics and mechanism in the extraction of citric acid from aqueous solutions with tri-n-octylamine was studied in the temperature range of 298-328 K. The widely used acidic metal extractant bis(2-ethylhexyl)phosphoric acid (D2EHPA) was selected as the model organic acid. Although citric acid was not extractable with D2EHPA alone, it was shown that the presence of D2EHPA could accelerate both rates of forward extraction and back extraction for the title system under the conditions studied. The rate equations for the formation and dissociation of citric acid-amine complexes were obtained, and a possible reaction mechanism was proposed and discussed. In addition, the effect of temperature on the reaction kinetics was examined and the activation energies were determined.