Fischer-Tropsch Synthesis (FTS) for olefin production from syngas was studied on Fe-Cu-K catalysts supported on ZSM-5 with three different Si/Al ratios. The catalysts were prepared by slurry-impregnation method of metallic components, and were characterized by BET surface area. XRD, hydrogen TPR and ammonia TPD. Fe-Cu-K/ZSM-5 catalyst with a low Si/Al ratio (25) is found to be superior to the other catalysts in terms of better C-2-C-4 selectivity in the FTS products and higher olefin/(olefin + paraffin) ratio in C-2-C-4 because of the facile formation of iron carbide during FTS reaction and also due to a larger number of weak acidic sites that are present in these catalysts. (C) 2009 Elsevier B.V. All rights reserved.