Intelligent self-assembly of nanobuilding blocks during the formation of Ni(OH)(2) single crystals with concave polyhedron structure was studied. The nickel hydroxide nanoplates pile up together with the aid of hydrazine molecules and grow along the [001] direction to form the brand-new geometry of concave polyhedrons. The novel nanostructure looks like a regularly twisted triangular prism wringed smoothly in the middle and could be attributed to the inherent spatial asymmetry of the nickel hydroxide crystal structure and the hydrogen bonds linked with the added hydrazine molecules. On the basis of the putative mechanism, polyhedrons with different longitudinal sizes (0.3-1 mu m) were synthesized by adjusting the quantities of hydrazine. We also obtained NiO polyhedron crystals with similarly piled plates by calcinations of the Ni(OH)(2) polyhedrons. Our preliminary electrochemical experiments show that the Ni(OH)(2) polyhedrons have potential applications in electrochemical storage.