A facile composite-hydroxide-mediated synthesis method is adopted to prepare ultralong, single-crystalline, hexagonal structured La(OH)(3) nanobelts. The detectable conductive behavior of a single La(OH)(3) nanobelt promises their potential application in sensors. La2O3 nanobelts can be obtained by calcination of the La(OH)(3) nanobelts. Both types of nanobelts fluoresce with purple light under UV excitation, which may be used in biological labeling.