The domain switching at the nanoscale is studied at both -Z and +Z surfaces of a lithium niobate crystal. A remarkable difference between both surfaces is experimentally observed by scanning probe microscopy, and is theoretically analyzed by the structural property and the chemical bonding structure of the lithium niobate crystal. The domain switching at the -Z surface is much easier and more stable than that at the +Z surface, which makes lithium niobate crystals have potential applications in the future domain engineering, especially at the nanoscale level. (C) 2003 Elsevier B.V. All rights reserved.