The effects of thioglycolic acid (TGA) on the rest potential and zeta potential of sulphide minerals were studied and the electrochemical mechanism of TGA depressing sulphide minerals was put forward. Results of flotation test show that galena, pyrite and chalcopyrite can be well depressed by TGA, but sphalerite and arsenopyrite can not be depressed. Tests also show that TGA has a little influence on zeta potential of sulfide minerals covered by xanthate coatings and TGA can lower the rest potential of sulphide minerals. The electrochemical mechanism of TGA depressing sulphide minerals is that the dixanthogen adsorbing on the mineral surface will be unstable and reduced when rest potential value of sulphide mineral ( φ MS ) is less than the reversible potential of reduction of dixanthogen to xanthate φ X -｜X 2 in the presence of TGA, flotability of sulphide mineral becomes weak; inversely, the coatings of dixanthogen on mineral surface will keep stable when φ MS > φ X -｜X 2 , sulphide mineral keeps flotability. In the system of mixed minerals, the electrochemical condition of separation of two sulphide minerals by TGA is φ MS1 < φ X -｜X 2 ( φ X -｜PbX 2 )< φ MS2 . [ The effects of thioglycolic acid (TGA) on the rest potential and zeta potential of sulphide minerals were studied and the electrochemical mechanism of TGA depressing sulphide minerals was put forward. Results of flotation test show that galena, pyrite and chalcopyrite can be well depressed by TGA But sphalerite and arsenopyrite can not be depressed. Tests also show that TGA has a little influence on zeta potential of sulfide minerals covered by xanthate coatings and TGA can lower the rest potential of sulphide minerals. The electrochemical mechanism of TGA depressing sulfur minerals is that the dixanthogen adsorbing on the mineral surface will be unstable and reduced when rest potential value of sulphide mineral (φ MS) is less than the reversible potential of reduction of dixanthogen to xanthate φ X - | X 2 in the presence of TGA, flotability of sulphide mineral becomes weak; inversely, the coatings of dixanthogen on mineral surface will keep stable when In the system of mixed minerals, the condition of the separation of two sulphide minerals by TGA is φ MS1 <φ X - | X 2 (φ X - | PbX 2 ) <φ MS2. [