The formation of nanosized stable iron-containing suspensions for implementing Fischer-Tropsch synthesis in the three-phase system is studied. The introduction of a polymer component in the composition of the dispersion medium is favorable for formation of particles of the dispersed phase of catalytic suspension with a size of nearly 170 nm. It is shown that the concentration of polyacrylonitrile in the composite metal-polymer systems affects their catalytic and physicochemical properties. Optimization of the catalyst system composition with respect to the content of the polymer component in the dispersion medium makes it possible to increase the yield of target products of Fischer-Tropsch synthesis in the studied temperature range by 30-35% compared with the system synthesized without any polymer component.