Domain switching behaviors of BaTiO3 single crystal in humidity conditions were studied by polarized light microscopy (PLM) and atomic force microscopy (AFM). The results showed that the low humidity has no effect on both a-b domain configuration and a-c domain configuration under sustained load. However, the high humidity can promote a domain switching to c domain under sustained load. The difference of energy reduction induced by H2O molecules between c domains and a(b) domains leads to this phenomenon. (C) 2008 Elsevier B.V. All rights reserved.