The present study was aimed to investigate the morphological and phase transformations of hydrothermally prepared titanate nanotubes (TNTs) in supercritical water (SCW). We found that single-crystalline anatase nanocrystals including rhombic nanoparticles with the ends faceted with (101) facets and spindle-shaped nanorods mainly exposing (010) facets were rapidly generated in 10 min, of which the thicknesses were less than 5 nm. The morphologies and crystal forms of products treated for 6 and 8 min were investigated, showing that the outside nanotube walls were gradually decomposed meanwhile the inside tubular structures underwent a local shrinkage, followed by spontaneous phase transformations. We proposed that TNTs were transformed into anatase nanocrystals by two simultaneous processes. One is a dissolution-nucleation and crystal growth while the other is an in situ nucleation and crystal growth, resulting in the formation of rhombic and spindle-shaped morphologies, respectively. (C) 2013 Elsevier B.V. All rights reserved.