The distribution of dysprosium (Ⅲ) between aqueous nitric acid solution and 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (PC-88A) has been measured in the range of an initial aqueous Dy (Ⅲ) concentration from 1.0 × 10-3 to 1.0 × 10-1 kmol/m3 and PC88A concentration from 5 vol% to 20 vol% in the diluent Shellsol D70.The data obtained were used to develop a chemically-based model to predict the equilibrium distribution ratios of Dy (Ⅲ) between aqueous and organic phases.The extraction equilibrium constant of dysprosium was determined to be 253 (kmol/m3)-2 with consideration of the activity coefficients of the inorganic ions and the effective concentration of the extractant.The extraction from hydrochloric acid and sulfuric acid was also investigated.