We present the results of self-consistent LMTO-ASA band structure calculations for SrNbO_3.4 based on the LDA. Eight bands per spin cut the Fermi surface. In accordance with experiment, we obtain a low density of states at the Fermi level, rising steeply with increasing energy. This explains qualitatively the low susceptibility found in this material. Similar to the simple perovskite structure SrNbO₃ , the conduction band complex is separated from the 5.6 eV wide valence band region by a gap of 1.7 eV. The spatial charge distribution shows that the bonding between the niobium and the oxygen atoms within the two-dimensional octahedral network is of primarily ionic character. A band complex of width 3.45 eV found at 17 eV below E_F is due to the O 2s states. The reasonable agreement between our calculated XAS cross sections for different light polarizations with recent experimental results suggest that an LDA treatment of this class of substances is appropriate, whereas Coulomb correlations play a minor role.