The laws governing the formation of nanoscale iron-containing disperse systems with a dispersed-phase particle size of 2-256 nm have been studied. The main features of the Fischer-Tropsch (FT) synthesis of synthetic hydrocarbons (HCs) in the presence of these systems have been revealed; the effect of the active phase concentration in the slurry on the selectivity for products with the C11+ chain length has been determined. It has been shown that a decrease in the particle size of the disperse system leads to an increase in the resistance of the iron carbide phase to oxidation by oxygen-containing products formed in the HC synthesis reaction.