A series of precipitated Fe/Cu/K/SiO2 Fischer-Tropsch synthesis (FTS) catalysts incorporated with the magnesium promoter were prepared by the combination of coprecipitation and spray-drying technology. The catalysts were characterized by using N-2 physisorption, H-2 or CO temperature-programmed reduction (TPR), X-ray diffraction (XRD), and Mossbauer spectroscopy (MES) methods. The results show that the addition of the magnesium promoter increases the BET surface area of the catalyst, and leads to the formation of the relatively smaller crystallite, size of alpha-Fe2O3 in the catalysts, facilitating the reduction and carburization. The extent of carburization increases with the increase of the magnesium content, and passes through a maximum at an Mg/Fe weight ratio of 0.07. The FTS performance of the catalyst were tested in a fixed bed reactor under the conditions of 250 degrees C, 2.0 MPa and 2000 h(-1) for 230 h on stream with syngas (molar ratio, H-2/CO = 2) used as feed gas. The results indicate that an appropriate amount of magnesium can improve the activity and stability of the catalysts, enhance the selectivity to C-5-C-11 and increase the space time yield Of C-5(+) hydrocarbon. The magnesium promoter can also slightly inhibit the activity of WGS, resulting in the decline of CO, selectivity and increase of the carbon utilization. However, excessive addition of the magnesium promoter will lead to a rapid deactivation of the catalyst. The optimal catalyst with Mg/Fe = 0.07 (M-3) has high activity and good stability, and keeps the selectivities of effective hydrocarbons ((C2C4=)-C-= + C-5(+)) and CH4 at about 83% and 8%, respectively, during the entire run period. (c) 2005 Elsevier B.V. All rights reserved.