Spectroscopic ellipsometry over the photon energy 1.5–5.0 eV is used to derive the dielectric function of V2O5 nanocrystalline films deposited by plasma-enhanced chemical vapor deposition. The dispersion in the optical response is described by a combination of Lorentzian oscillators. The results are obtained from a microstructure-dependent model, which considers the anisotropy of the V2O5 crystallites into the bulk film, as well as the presence of interface and surface roughness layers. The variation of the V2O5 thin-film dielectric function upon film crystallinity, going from pure nanocrystalline to amorphous material, is also investigated. © 2000 American Institute of Physics.