In extraction of ferric ion with D 2 EHPA, concentrations of ferric ion near the interface were measured by a position-scanning spectrophotometer, and the dependencies of reaction rate on ferric ion, extractant dimer, and hydrogen ion concentrations were elucidated. Based on the experimental results, with the aid of concentration dependencies of interfacial tension, it was clarified that 1) in the extraction region, emulsions are formed in the organic phase, 2) the extractant reacts with ferric ion to form a 1 : 2 intermediate complex, 3) the rate of reaction is proportional to ferric ion concentration and is inversely proportional to hydrogen ion concentration, showing a first-order dependency on dimer extractant concentration in lower extractant concentrations, but zero-order in higher extractant concentrations, and 4) the rate of reaction can be explained by assuming that the kinetic model in which the primary 1 : 2 intermediate complex formation reaction between ferric ion and adsorbed dimer extractant is rate-determining.