Vanadium pentoxide nanoparticles with different sizes were prepared by a microwave-assisted hydrothermal reduction combined with subsequent annealing treatment. The surface enhanced Raman spectroscopy (SERS) activity of rhodamine 6G (R6G) over V2O5 nanoparticles was investigated. It was found that the SERS activity of R6G is size-dependent, and the smaller the nanoparticle size the higher the SERS activity. The V2O5 nanoparticles with an average size about 42 nm have a detecting limit better than 10(-8) M R6G. The SERS activity of R6G over V2O5 nanoparticles is also excitation wavelength-dependent, and the 532 nm laser displays an optimal SERS activity because of the energy matching between V2O5 nanoparticles and R6G molecules in the photo-induced charge transfer process. (C) 2015 Elsevier B.V. All rights reserved.