Abstract: Two shape-defined nano-structured Fe₃O₄ catalysts such as Nano-Microsphere (FNM) and Nano-Flake (FNF) were prepared by a simple solvothermal method. The effects of precursor type on Fe₃O₄ crystal morphology was studied. It is found that the rate of nucleation and crystal growth have a crucial influence on the particle morphology. Compared to the traditional Fe catalyst, the shape-defined nano Fe₃O₄ catalysts could be easily reduced and transferred into active phases, resulting in higher Fischer-Tropsch synthesis (F-T) activity and C₅₊ selectivity. Especially, the FNM catalyst displayed higher catalytic activity and stability than the FNF catalyst. It was found that the FNF catalyst was more favorable to agglomeration because of shape change of the flakes. In addition, the results indicate that the hydrocarbon selectivity is strongly affected by the particle morphology.