A general permeation model for the separation of thorium by liquid emulsion membrane (LEM), using theonyletrichloroacetone HTTA as a carrier is presented. The internal mass transfer in the W/O emulsion drop, the external mass transfer around the drop, the rates of formation, and the decomposition of the complex at the external aqueous-organic interface were considered. Further, the leakage of the internal aqueous phase to the external phase due to the membrane break-up is also taken into account. The batch extraction of thorium using HTTA as a carrier was carried out under various experimental conditions. It is found that the extraction rates can be satisfactorily simulated by the proposed model.