The relationship between the nature of organic solvents and the extractability of metal complexes has been reviewed. The solvation of metal complexes in organic solvents, which is one of the most important factors to improve the extractability, has also been explained. In addition, recent topics such as adsorption of extractants and metal complexes on the liquid-liquid interface, and the oxidation of metal ions in complexes in organic solvents are described and the role of such phenomena on the solvent extraction of the metal is considered.