The vacuum residual from Iranian Light crude oil are separated into a series of 16 narrow fractionsaccording to the molecular weight by the supercritical fluid extraction and fractional (SFEF) technology. Thechemical element and the UV spectrum of each fraction are analyzed. The effects of several factors on the interfacialtension are investigated, which are the fraction concentration in oil phase, the ratio of oil component, the saltsdissolved in the water phase and the pH value. The interfacial tension decreases rapidly as the concentration of theresidual fraction in the oil increases, showing a higher interfacial activity of the fraction. The interfacial tensionchanges, as the amount of absorption or the state of the fractions in the interface changes resulting from differentratios of oil, different kinds or concentrations of salts in water, and different pH values. It is concluded that theinterfacial tension changes regularly, corresponding to the regular molecular parameters of the vacuum residualf The vacuum residual from Iranian Light crude oil are separated into a series of 16 narrow fractionsaccording to the molecular weight by the supercritical fluid extraction and fractional (SFEF) technology. The chemical elements and the UV spectrum of each fraction are analyzed. The effects of several factors on the interfacialtension are investigated, which are the fraction concentration in oil phase, the ratio of oil component, the salts resolved in the water phase and the pH value. The interfacial tension decreases rapidly as the concentration of the residual fraction in the oil increases, showing a the interfacial activity of the fraction. the interfacial tension ofchanges, as the amount of absorption or the state of the fractions in the interface changes resulting from differentratios of oil, different kinds or concentrations of salts in water, and different pH values. the interfacial tension changes regularly, corresponding to the regular molecular parameters of th e vacuum residualf