Abstract: The solvent extraction of cerium (Ⅲ) by 1-( 2-pyridylazo )-2-naphthol ( PAN or HL ) in chloroform has been studied as a function of contact time, the pH of aqueous phase and the concentration of the extractant in the organic phase. The results obtained suggest that the mechanism for the extraction reaction isFrom the distribution coefficient D, extraction equilibrium constant Kex of reaction, and pH 0.5 are estimated.