Abstract: Some important peculiarities of interfacial mass transfer with chemical reactions in liquid-liquid systems were explained with the help of interfacial dispersed zones (IDZ) formation.A sudden and sharp increase in HCl extraction rate by tri( n -dodecyl)amine was explained by means of a new dispersed phase formation inside of the organic layers adjacent to the interphase.This process of water mirodroplets formation is accompanied with the change of local equilibrium constant and concentration gradient.Surface-active substances(SAS) added to the system could essentially affect the rate of interfacial diffusion because of change of number and dimension of microparticles inside of IDZ.The rate of interfacial diffusion increases if SAS stabilize IDZ and (or) enhance adsorption of reactants on the surface of microparticles of IDZ.The opposite situation can be observed if SAS destabilize IDZ and (or) decrease adsorption of reactants.These effects were found in extraction and stripping of Cu ²⁺ in the system with 2-hydroxi-5-octylbezo phenonoxime.