A series of micro-mesoporous ZSM-5/MCM-41 composite molecular sieves were prepared by combining a microporous zeolite silica source with nano self-assembly methods, and characterized by SEM, TEM, XRD, N-2 adsorption and desorption, TPD of ammonia, and their catalytic performance for the dehydration of methanol to dimethyl ether (DME) in a fixed bed microreactor at atmospheric pressure. Among these catalysts, the ZSM-5/MCM-41 sample alkali-treated with 1.5 mol/L NaOH solution, in which the relative crystallinity of ZSM-5 and MCM-41 are 54.5% and 30.5%, respectively, gave the best activity (X-MeOH > 80%) with 100% selectivity and a long lifetime in a wide range of temperature from 190 degrees C to 300 degrees C. From the characterization and activity data, the formation mechanism of the micro-mesoporous composite molecular sieves was proposed to be a liquid-crystal templating mechanism. (C) 2011 Elsevier B.V. All rights reserved.