Catalytic conversion of i-butane over Zn-modified HZSM-5 catalyst was systematically investigated at different reaction pressures. A special fixed-bed reactor involving a vacuum unit which could modulate reaction pressure from subatmospheric to positive pressure was used. Results show that reaction pressure can change the initial activation and subsequent reaction paths of i-butane over Zn/HZSM-5 catalyst. At subatmospheric pressure, the decrease in reaction pressure favors the dehydrogenation of i-butane, meanwhile inhibits both the cracking of i-butane and the secondary reactions such as the oligomerization, cracking and aromatization. Consequently, the selectivities to the undesired by-products (methane and ethane) are notably abated, and the selectivities to the desired products (ethylene, propylene and aromatics) significantly increase. Although space velocity affects the reaction paths for i-butane conversion, the change in reaction pressure has a more profound effect on the reaction paths. (C) 2012 Elsevier B.V. All rights reserved.