Dynamic interfacial tension measurements were used to investigate the kinetics of the diffusion/adsorption of surfactant molecules at the benzene-water interface, Measurements were performed on stearic acid and capric acid by the pendant drop method at both benzene-acidic aqueous and benzene-basic aqueous interfaces. The process takes place by different mechanisms in the acidic and basic aqueous phases, The mechanism of the interfacial neutralization of stearic acid with sodium hydroxide is discussed.