Titanosilicate ETS-10 crystals were prepared by hydrothermal synthesis varying Ti source (TiCl(3) and commercial TiO(2)-anatase). time in autoclave and seeding with previously prepared ETS-10 crystals. The crystalline powders were characterized by X-ray diffraction, N(2) adsorption, thermogravimetric analysis, and scanning and transmission electron microscopies. Control of the particle size of ETS-10 crystals ranging from 0.32 mu m x 0.41 mu m to 16.4 mu m x 32.5 mu m was successfully achieved varying the seeding and synthesis conditions. In particular, it was found that the use of TiO(2)-anatase alone or together with TiCl(3) promotes heterogeneous primary nucleation. Transmission electron microscopy demonstrated that the largest crystals obtained here were twinned. (C) 2009 Elsevier Ltd. All rights reserved.