In this work, the conversions of ethanol to propylene and ethylene to propylene were investigated over H-ZSM-5 zeolite catalysts with different SiO2/Al2O3ratios (80 and 280). The effect of operating conditions (contact time and reaction pressure) has been studied. Special attention has been paid to the effect of reaction pressure on the propylene yield, space time yield and catalyst deactivation. Results show that the H-ZSM-5(280) catalyst was more stable for the ethanol or ethylene conversion reaction. High operating pressure favors the propylene production. However, the higher pressure leads to faster coking.