Zeolite L thin films were fabricated by applying fine zeolite L seed crystals on glass substrates and then hydrothermally treating the seeded substrates in reaction sots. The influence of anisotropic growth of the seed crystals on the orientation of the films was examined. The reaction sots were prepared by mixing KOH, Al, colloidal silica, and water. With increasing the amount of the KOH in the sots or with decreasing the hydrothermal temperature, the zeolite L crystals obtained from the sots changed from a rod-like shape to a clam-like one, indicating a decrease in the relative rate of the growth along the c-axis of zeolite L with a hexagonal lattice to one normal to the c-axis. For the film fabricated at a small amount of KOH or at a high hydrothermal temperature, the c-axis of the zeolite crystals was oriented normal to the substrate. The fabrication at a large amount of KOH or at a low hydrothermal temperature led to films consisting of zeolite crystals whose c-axis is parallel to the substrate. When the aspect ratio of the precipitated crystals decreased to about one, the c-axis of the zeolite crystals in the films became parallel to the substrate. (C) 2007 Elsevier B.V. All rights reserved.