Urchin-like VO2(B) nanostructures composed of radially aligned nanobelts have been synthesized by the homogeneous reduction reaction between peroxovanadic acid and oxalic acid under hydrothermal conditions. The influences of synthetic parameters, such as reaction times and the concentration of oxalic acid, on the morphologies and crystals of the resulting products have been investigated. The formation of VO2(B) nanostructures undergoes a reduction-dehydration phase-transition and disassembly process. As the reaction time increases from 2 to 6 h, the diameters of urchin-like V10O24 center dot 12H(2)O nanostructures increase from 1-2 mu m to 3-6 mu m. After 12 h, urchin-like V10O24 center dot 12H(2)O nanostructures can be transformed in situ into VO2(B) nanostructures composed of radially aligned nanobelts, which can be described by a possible reduction-dehydration phase-transition process. The urchin-like VO2(B) nanostructures are disassembled into dissociated VO2(B) nanobelts with the reaction time increased to 24 h. The shapes of the dissociated VO2(B) nanobelts can be controlled by adjusting the concentration of oxalic acid.