The synergistic extraction of UO2(II) in a chloroform solution of propionic, butyric and valeric acids (HA) in the presence of some aliphatic and aromatic amines (B) has been investigated. The effect of various variables, like the concentration of hydrogen and metal ion, carboxylic acid and amine on extraction has been studied. The composition of the synergistic adducts has been determined on the basis of slope analysis and the species is proposed to be UO2A2B2 2HA. The extraction constants (Kex) have been calculated and the relative effectiveness of the amines as synergists is compared. Extraction data have been used to separate UO2(II) from lanthanides, like Ce(III), Nd(III), Gd(III), Eu(III) and Yb(III).