The behaviour of a HZSM-5 zeolite (SiO2/Al2O3 = 30) in several time treatments with 0.2 Nt NaOH solution has been studied for the transformation of bioethanol into hydrocarbons in an isothermal fixed bed reactor and in the 225-425 degrees C range. A short treatment (for 10 min) decreases the acid strength of the sites horn 135 kJ(mol of NH3)(-1) to 125 kJ (mol of NH3)(-1), which is effective for increasing the selectivity of propene and butenes and for attenuating the deactivation by coke. This catalyst allows obtaining a yield of 30 wt% of propene + butanes at 400 degrees C with 136 (g of catalyst) h (gethanol)(-1) and a feed of ethanol/water with 5 wt% water. The operation in reaction-regeneration cycles can be carried out continuously without irreversible deactivation of the catalyst, which means not exceeding extreme conditions in the reaction step 375 degrees C and 400 degrees C for water contents in the feed of 75 wt% and 5 wt%, respectively More severe treatments decrease the hydrothermal stability of the zeolite (C) 2010 Elseviei B V All rights reserved