Studies on the effect of temperature on the liquid-liquid extraction behaviour of a trivalent actinide ion, Am 3+ and a trivalent lanthanide ion, Eu 3+ using a "S"-donor soft ligand, bis (2,4,4-trimethylpentyl) dithiophosphinic acid (Cyanex ® -301) were carried out. The temperature effect on the enhancement in extraction as well as the selectivity which occurred in the presence of neutral soft donor auxiliary ligands with "N" donor atoms viz., bipyridyl (bipy) and 1,10-phenanthroline (phen) was also investigated. Thermodynamic parameters like the changes in the extraction enthalpy (∆H • ), entropy (∆S • ) and free energies (∆G • ) for both the binary as well as ternary extraction systems were obtained. These thermodynamic parameters could explain the nature of the species extracted with both Am(III) and Eu(III).