Alumina supported 5% Co catalyst was prepared, by the controlled nanocrystal deposition method using oleic acid as a capping agent, and tested for its activity and selectivity in Fischer-Tropsch synthesis. The catalyst exhibited facile reducibility of the cobalt species. The CO conversion and C5+ selectivity obtained on this size-controlled catalyst were higher than those observed on the catalysts prepared by impregnation and precipitation techniques. Decrease in the mobility of the nanoparticle towards the tetrahedral sites of alumina could be the reason for high reducibility, as the formation of cobalt aluminate was found to be considerably reduced during temperature programmed reduction.