The present study was undertaken to investigate the catalytic behavior of an industrial iron catalyst (Fe/Cu/K/SiO2) prepared from ferrous sulfate precursor for Fischer - Tropsch (FT) synthesis, in which different amount of Fe3O4 coexist with alpha-Fe2O3. The catalyst samples were characterized by BET, XRD, H-2-TPR and Mossbauer effect spectroscopy ( MES). The FT synthesis performance of the catalysts were carried out in a fixed bed reactor (FBR) under reaction conditions of 250 degrees C, 1.5 MPa, 2.0 nL/g-cat/ h, and H-2/CO= 2/ 1 for 200 h. The results from XRD and MES for the catalyst samples of pre- and post-reduction indicate that more iron carbides form in the catalysts that have lower Fe3O4 contents. H-2-TPR for the catalysts displays that Fe3O4 may facilitate the reduction of catalysts only when it was highly dispersed. FT reaction study in the FBR shows that the catalysts become more active with the decrease of Fe3O4 contents in the catalysts. However, the catalyst with certain amount of highly dispersed Fe3O4 exhibited high FT synthesis activity with CO conversion more than 75%. The catalyst also displayed much less olefins selectivity. A comparison of FTS performances of one of these catalysts with some known catalysts was also made in this paper.