The solvent extraction of KAu(CN)2 from alkaline solution by quaternary ammonium salts (trialkyl-methylammonium chloride or cetyltrimethylammonium bromide) was investigated by means of 198Au radioactive tracer method. Various parameters, such as the gold (I) concentration in aqueous phase, the modifier, emulsification at the interface of two phases, and phase ratio used in the extraction of gold (I) were studied. The results demonstrate that almost all gold (I) in the aqueous phase was practically extracted into the organic phase. The water content in the organic phase decreased significantly with increase of gold (I) concentration using long chain alcohol as modifier, in contrast with the system with tributyl phosphate (TBP) as modifier. Emulsification at the interface of two phases decreases with an increase of modifier concentration in the organic phase or with the addition of a small amount of lysozyme into the aqueous phase. The method with 198Au tracer can be directly used to determine the Au(I) co The solvent extraction of KAu (CN) 2 from alkaline solution by quaternary ammonium salts (trialkyl-methylammonium chloride or cetyltrimethylammonium bromide) was investigated by means of 198 Au radioactive tracer method. Various parameters, such as the gold (I) concentration in aqueous phase, the modifier, emulsification at the interface of two phases, and phase ratio used in the extraction of gold (I) were studied. The results demonstrate that almost all gold (I) in the aqueous phase was practically extracted into the organic phase. The water content in the organic phase decreased significantly with increase of gold (I) concentration using long chain alcohol as modifier, in contrast with the system with tributyl phosphate (TBP) as modifier. Emulsification at the interface of two decreases with an increase of modifier concentration in the organic phase or with the addition of a small amount of lysozyme into the aqueous phase. The method with 198 Au tracer can be directly used to det ermine the Au (I) co