VO2 (B) nanostructures were synthesized via a facile hydrothermal process using V2O5 as source material and oxalic acid as reductant. Three nanostructures of nanorods, nanocarambolas and nanobundles were found existing in the products, and a continuous changing of morphology was found in the synthesis process, during which the proportion of these three types of nanostructures can be adjusted by altering the concentrations of oxalic acid. The microstructures were evaluated using X-ray diffraction and scanning and transmission electron microscopies, respectively. FE properties measurement of these three types of nanostructures showed that the nanobundles have the best field emission performance with a turn-on field of similar to 1.4 V/mu m and a threshold field of similar to 5.38 V/mu m. These characteristics make VO2 (B) nanostructures a competitive cathode material in field emission devices. (C) 2011 Elsevier B. V. All rights reserved.