The symmetry and disorder of the Eu3+ site was investigated in some phosphate and borate glasses by means of 151Eu Mössbauer spectroscopy. The quadrupole interaction parameter, which is due to the distortion of the Eu site compared to a cubic symmetry, has been measured together with the asymmetry parameter, which points out the absence of a threefold or fourfold axis of symmetry at the rare earth site. The correlation of the isomer shift with the optical basicity of the glass indicates a covalent component with 6s character in the Eu-O bond. The axial component of the electric field gradient at the Eu site is also correlated with the optical basicity.