Abstract: The work investigates the technique conditions for the separation of An(Ⅲ) and Ln (Ⅲ) withinthe acidity range of 0. 2--0. 5 mol/l HNO_3. The effects of varying HDEHP, DTPA, H~+ and initialmetal ion concentrations, and temperature are studied. The results show that the distribution ratio ofAm(Ⅲ), Gd(Ⅲ) and Eu(Ⅲ) are proportional to the second power of HDEHP concentration, and in-versely proportional to the third power of H~+ concentration, respectively. The extraction enthalpies ofAm(Ⅲ), Gd(Ⅲ) and Eu(Ⅲ) are -7.1×10~3 J·mol~(-1), -9.2×10~3 J·mol~(-1) and -1.9×10~3 J·mol~(-1) in turn. 1.0 mol/l HDEHP--kerosen is used for coextraction of An (Ⅲ) and Ln(Ⅲ), and a lac-tic acid--DTPA mixture solution is used for selective striping of An(Ⅲ). Counter--current cascade ex-periments are performed. Nearly 100% An(Ⅲ) is recovered, less than 3% Ln(Ⅲ) remains with An(Ⅲ). A conceptual flowsheet for the separation is suggested.