The extraction behavior of La3+, Sm3+, Dy3+, and Yb3+ in sodium acetate-acetic acid medium was studied with tri-n-butyl phosphate (TBP) at 60 ℃ using paraffin wax as a diluent. The extraction percentage is greater than 85% in the pH range of 6 to 8. The result of slope analysis method indicates that the compositions of the extracted species are different between the light and heavy rare earths. The formula of the extracted species is found to be La(TBP)(OH)(Ac)2 for La3+ and Yb(TBP)(OH)3 for Yb3+. The effects of extracting time, the concentration of TBP in the organic phase and salts on the extraction efficiency were also discussed. The extraction behavior of La3 +, Sm3 +, Dy3 +, and Yb3 + in sodium acetate-acetic acid medium was studied with tri-n-butyl phosphate (TBP) at 60 ° C using paraffin wax as a diluent. The extraction percentage is greater than 85% in the pH range of 6 to 8. The result of slope analysis method indicates that the compositions of the extracted species are different between the light and heavy rare earths. The formula of the extracted species is found to be La (TBP) (OH) ( Ac) 2 for La3 + and Yb (TBP) (OH) 3 for Yb3 +. The effects of extracting time, the concentration of TBP in the organic phase and salts on the extraction efficiency were also discussed.