High performance silicalite-1 membranes on outer surface of macroprous alpha-Al2O3 supports were synthesized by counter-diffusion secondary growth (CDSG). Different from the conventional synthesis methods by which the silica source (tetraethyl orthosilicate) and the template agent (tetra-propyl ammonium bromide) were mixed together to form the synthesis solution, this method introduced silica source and template agent from the opposite direction of a support wall, resulting in good membrane structures and properties as well as reduced chemical consumption. The correlation between particle size of seeds and the pore size of supports was optimized, and its influence on the morphology and permeation property of the as-prepared membranes was also investigated. Results showed the as-prepared membranes were typical silicalite-1 membranes without any other phase. The membranes were dense, continuous without obvious defects, displaying good permeation property. The H-2 permeance and H-2/SF6 ideal permselectivity for the membrane prepared under optimized parameters were up to 7.5 x 10(-7) mol m(-2) s(-1) Pa-1 and 103 at 298 K under 0.1 MPa pressure drop, respectively. Moreover, by the CDSG method the consumption of the template can be greatly reduced. (C) 2009 Elsevier B.V. All rights reserved.