Abstract: PTSOis abbreviated from di-p-tolyl sulphoxide having a >S=Ogroup and is a neutral extractant.We have studied the separation behaviour of Au (Ⅲ) with other elements on a column packed with silica gel loaded with PTSOsince 1981 and have proved that PTSOis a new specific stationary phase for saparation and concentration of gold.The behaviour and mechanism using PTSOto extract gold were studied first in this paper by atomic-absorption spectrophotometry, ultraviolet spectrophotometry and infra-red spectrophotometry.The mechanism has been further improved by the electroconductivity method.The distribution ratios increase with increased HCl concentrations and the salt strength in aqueous phase but decrease with increasing temperatures.The constituent of the extracted complex is established as Au:H:Cl:PTSO=1:l:4:3 and its possible structure form is suggested.