The solvent extraction of lanthanum(III) and europium(III) by aminooctyldimethylene diphosphonic acid from nitrate media was investigated. The extraction percent of lanthanum(III) and europium(III) was measured as a function of various parameters such as: volume ratio, shaking time, the concentration of aminooctyldimethylene diphosphonic acid, ionic strength and media pH. The metal concentration in the aqueous phase before and after extraction was determined spectrophotometrically by the Arsenazo III method. The extracted species and equilibrium extraction equations were determined by the slope analysis method. It was found that adding KNO 3 at a concentration of 0.1 M significantly enhances the extraction yield for lanthanum(III) and europium(III). Decreasing the media pH caused a gradual decrease of extraction yields. The obtained results showed that extraction of lanthanum(III) and europium(III) from nitrate media using aminooctyldimethylene diphosphonic acid in chloroform is quantitative under well-defined conditions.