Structural defects and thermodynamics of vitreous GeO2 nanoparticles have been studied in spherical models of different sizes ranged from 2 to 5 nm. Models have been obtained by cooling from the melts via using molecular dynamics (MD) method with the ab initio pair interatomic potentials. Structural properties were investigated via partial radial distribution function (PRDF), interatomic distances, bond-angle and coordination number distributions. Surface and core structure of amorphous GeO2 nanoparticles have been studied in details. Structural defects and their role in structure and properties of nanoparticles have been analyzed and discussed. We found temperature (and size) dependence of potential energy, surface energy of GeO2 nanoparticles. We also found the size dependence of glass transition temperature of nanoparticles. (C) 2010 Elsevier B.V. All rights reserved.