The mesoporous silica spheres with bimodal pore structure were successfully prepared from silica/hyperbranched polyester (Boltorn (TM) H20, H20) and silica/glycidoxy-propyltrimethoxysilane modified H20 (H20M) using a simple sol-gel process, and characterized with TEM, FTIR, XPS, TGA, DSC, and N-2-BET computation. The effects of organic phase content on the characters of the formed mesoporous silica spheres were investigated. The results showed that the silica spheres prepared from silica/H20M have a bigger particle size, specific surface area and porous volume, and narrower bimodal pore-volume distribution compared with that formed by silica/H20. (c) 2006 Elsevier Inc. All rights reserved.