Five silicalite-1 zeolite seeds of around 100 run, 600 nm, 1.5 mu m, 3.0 mu m and 7.5 mu m were prepared. The preparation of porous alpha-alumina supports seeded using slip-casting technique and respective zeolite silicalite-1 membranes regrown by hydrothermal synthesis was investigated for different seed sizes. The effects of seed sizes on the formation of seed layers and zeolite membranes were studies in detail. It has been found that seed sizes have important effects on the formation of seed layers that determines the quality of regrown zeolite membranes. The seed layer and the regrown membrane from smallest seed (100 nm) are most uniform and densest. With the increase of seed sizes (from 600 nm to 3 mu m), the seed layers and the membranes become coarser and the intergrowth of the membranes becomes poorer. Increasing synthesis temperature favors improving the crystal intergrowth of the membrane, reducing the voids and changing the orientation of crystal growth. The zeolite particles with the size of 600 nm and 1.5 mu m may act as seeds to form a continuous and uniform seed layer and membrane layer, whereas using zeolite seeds of 7.5 mu m, a continuous membrane cannot be obtained because of the formation of an incontinuous seed layer. (c) 2005 Elsevier B.V. All rights reserved.