Relevance. In recent years, polymer flooding technologies have been widely used in exploitation of oil and gas fields, especially in the later stages of field development. However, when operating reservoirs with elevated temperature of more than 70–80 °C and a high degree of salinity of formation water, many polymeric oil-displacing agents undergo rapid degradation, which leads to decrease in the level of hydrocarbon production. In this regard, one of the important problems is the creation and development of thermo- and salt-resistant polymeric materials and compositions based on them to increase the production of hydrocarbons in the oil and gas fields. The main aim of the research is to investigate the effect of formation water salinity on the physicochemical and filtration characteristics of polymer solutions and gels to enhance oil recovery. Methods. Viscosity of the polymer solutions and polymer gel were determined on Brookfield DV-II viscometer; shape and size of the polymer particles and polymer gel were studied on Hitachi S-400N scanning electron microscope; polymer size of molecular tangle Dh was measured on a wide-angle dynamic/static light scattering system Brookhaven BI-200SM (Brookhaven Instruments Cop., USA); physical modeling of fluid filtration at reservoir conditions was carried out on the filtration unit; determination of viscoelasticity and rheological properties of polymer solutions and gels was studied using a rheometer Harke 10. Results. The degree of mineralization of formation water has a significant effect on the viscosity of polymer solutions. Due to the fact that calcium and magnesium ions were preliminarily removed in partially demineralized water, the polymers have good solubility and the ability to increase the viscosity of the solutions. With increasing concentration of displacing agent, the viscosity of the solutions increases. Destructive effects of salts of formation water on polymers cause a significant decrease in viscosity of solutions of displacing agents. Due to the high degree of mineralization of partially demineralized water, a large amount of sodium chloride ions surround the molecular skeleton of the polymer of the displacing agent. The macromolecules of polymer P-1 have a predominantly two-dimensional network structure. The macromolecules of polymers P-2 and P-3 have a predominantly spatial three-dimensional network structure, in which some polymer molecular chains are broken and the network structure of polymers is defective. Compared with polymer P-3, the three-dimensional network structure of the polymer molecular aggregate P-4 has a clearer spatial structure. Comparing the physico-chemical properties of polymers P-1, P-2 and P-3, it follows that the coefficient of resistance and the coefficient of residual resistance for polymer P-1 are greater than for polymers P-2 and P-3. This is due to the fact that the salt-resistant polymer P-1 forms aggregates of the network structure due to intermolecular association, which leads to poor compatibility with core pores, and the resistance coefficient and residual resistance coefficient for polymer P-4 are the greatest the polymer mixture underwent reactions of intramolecular crosslinking of polymer molecules and Cr³⁺ cations, which led to a significant increase in the retention of the polymer solution, filtration resistance, injection pressure and to enhance oil recovery.