The transport behaviour of trivalent actinides, viz. Am3+, Cm3+ and lanthanides, viz. La3+, Eu3+, Tb3+, Ho3+, Yb3+ and Lu3+ across a polypropylene based supported liquid membrane containing Cyanex-301 (bis-(2,4,4-trimethyl pentyl)-dithiophosphinic acid) in n-dodecane as the carrier was investigated. The transport rates were in accord with their distribution data as seen from the solvent extraction studies. The trivalent actinides Am3+ and Cm3+ could be quantitatively separated from the lanthanides by this membrane based method in 4 and 20 h, respectively, with separation factor values in the range 108-4466. (C) 2005 Elsevier B.V. All rights reserved.