Аннотация:The viscosities of di-(2-ethylhexyl)phosphoric acid (D2EHPA)–samarium (europium, gadolinium) di-(2-ethylhexyl) phosphate–n-heptane (toluene, cyclohexane, n-hexane) solutions, which constitutean organic phase in processes of lanthanide extraction, are measured. A logarithmic model with an excess part in the Redlich–Kister form is shown to describe the rheological properties of the D2EHPA–rare-earth di-(2-ethylhexyl) phosphate–organic diluent systems, based on data on the D2EHPA–organic diluent binary subsystems and the viscosity of liquid rare-earth di-(2-ethylhexyl) phosphate.