Heteroepitaxial KNbO3 thin films and nanostructures were grown hydrothermally on (100)-oriented single-crystal SrTiO3 substrates at 125-200 degrees C in 15 M KOH solutions. The KNbO3 film grew with the orthorhombic structure and displayed both {110)(o) and (001) orientations as anisotropic lattice expansion reduced the difference in lattice mismatch seen by each orientation. After an initial period of approximately planar growth, the film gave rise to an array of nano-sized tower-like structures apparently growing by a dislocation-assisted mechanism. It is suggested that the anisotropic growth is further promoted by a combination of decreasing supersaturation and the increased effect of adsorbed impurities on the growth front. (c) 2005 Elsevier B.V. All rights reserved.