As a result of switching the growth from hexagonal disks to nanorods/nanobelts, single-crystalline 'nanocastles' of ZnO have been synthesized. This new structure was constructed by two basic parts: a sheet-like hexagonal crystal base and vertical nanorods/nanobelts surrounding the base as the 'walls' of the castle. Moreover, for the first time, ZnO nanorods with a triangular and diamond cross-sections were found growing on top of the nanocastles. The whole nanocastle structure was enclosed by the {0001} and {01 (1) over bar0} facets. This configuration is a new member in the family of ZnO nanostructures. The in situ morphology switching mechanism would be an useful technique for fabricating high quality heterostructures or interconnetts at nanometer scale. (c) 2006 Elsevier B.V. All rights reserved.