A novel sulfur-containing solvent extraction reagent, 3,3-diethylthietane (DETE) was synthesized and its extraction mechanism of platinum (IV) from aqueous hydrochloric acid solution was investigated at 30 °C in terms of the equilibrium distribution and extraction kinetics as well as its aqueous distribution and inter-facial adsorption equilibrium. Toluene was used as a diluent. It was elucidated that platinum(IV) is extracted as a solvated complex of the type, PtCl4-4DETE. DETE was found to have no inter-facial activity and the aqueous partition coefficient as high as 8.17xl0-4. Extraction rate was measured by using a vigorously stirred cell. It was of the first order with respect to DETE while it is 0th and inversely first order with respect to chloride ion in its low and high concentration region; this result was interpreted in terms of the classical hetero-phase homogeneous reaction model.