Conversion of methanol and dimethyl ether to propylene was investigated in a fixed-bed reactor using an extruded H-ZSM-5 catalyst embedded in a matrix of silica. Physical and chemical properties of these catalysts have been determined by SEM, N-2 adsorption-desorption, XRD, and NH3-TPD. Results showed that the amount of mesopores tends to vary with the extrusion process, which has a positive impact on propylene selectivity. Experiments were carried out at 515 A degrees C, with a weight hourly space velocity of 15 h(-1), and at different Si/Al ratios ranging from 60 to 560. Different reaction times and water concentrations ranging from 30 to 2400 min and 0 to 60 wt%. respectively were considered as well. Additional experiments with ethylene (or propylene) and water were performed to elucidate side reactions. The results highlighted that the Si/Al ratio had an effect on dimethyl ether conversion, likewise on the products selectivity and coke deposition. At higher Si/Al ratio, DME conversion and selectivity in propylene increased, while the coke deposition decreased. It seems that propylene selectivity increases with regards to reaction times. Also, addition of water in the stream facilitates olefins desorption, thus reducing the amount of side-products (light saturated paraffins). [GRAPHICS] .