In tin oxide nanostructures, oxygen vacancies (OVs) usually determine optical properties and thus exact identification of both OV concentration and type is crucial to exploration of more applications. Currently, the 755-778 cm(-1) Raman mode is frequently observed and arbitrarily attributed to E-u (LO) or B-2g mode. In this work, we examine the Raman spectra of SnO2 nanocrystals prepared by laser ablation method and find that the Raman peak blueshifts from 755 to 778 cm(-1) with increasing annealing temperature in O-2. Spectral analysis and density functional calculations disclose that crystal symmetry destruction by bridging OVs makes B-2g mode (778 cm(-1)) redshift gradually and finally occupy Eu (LO) mode position (755 cm(-1)). Thus, it should not be assigned to Eu (LO) mode. (C) 2015 Elsevier B.V. All rights reserved.