The features of the Fischer-Tropsch synthesis in the presence of 100Fe : 8A(l)2O(3) : 3K(2)O (parts by weight) catalyst nanoparticles under the slurry reactor conditions have been studied. The catalyst is prepared in situ and activated in the reactor. It has been found that during the preparation process, the catalyst reacts with the dispersion medium to form a structured system that is not liable to sedimentation. It is shown that the use of CO as a reducing agent makes it possible to increase the yield of liquid hydrocarbons by a factor of 1.5. An increase in the syngas pressure has almost no effect on the yield of liquid hydrocarbons; however, it gives the possibility of enhancing the catalyst efficiency up to 700 g/(kg Fe . h) at 40 atm. In conditions of a three-phase system, gasoline-fraction hydrocarbons, half of which consist of olefins, are mostly formed on the nanosized catalyst.