Modified Fischer-Tropsch (MFT) syntheses were carried out, to convert synthesis gas to C-4 hydrocarbons over Fe-Co/ZrO2(FT) and SO42-/ZrO2 (SZ) catalysts in a dual reactor system, keeping the FT to SZ catalysts ratio at 1:1.5.,Five Fe-Co/ZrO2 catalysts with different Fe and Co loading,, and SZ with 15 wt% SO42- were prepared and extensively characterized using various physico-chemical methods. The FT synthesis process was initially performed using a Fe-Co/ZrO2 catalyst in a single reactor and the effects of Fe and Co mass ratio, reaction temperature, space velocity on the production of C-4 hydrocarbons and C-2-C-4 olefins were investigated. Results indicated that a 3.71% Fe-8.76% Co/ZrO2 mixed oxide catalyst alone at 260degreesC and 5 h(-1) gave high selectivities of C-2-C-4 olefins (similar to26.1 wt%) and total C-4 hydrocarbon product (similar to16.2 wt%). The MFT process 150degreesC gave higher C4 (similar to31.6 wt%), isobutane (similar to22.9 wt%) and C-2-C-4 (31.1 wt%) selectivities.