The electronic structures of KNbO3were calculated within the density functional theory, and their evolution was analyzed as the crystal-field symmetry changes from cubic to rhombohedral via tetragonal phase. We carried out electron-energy loss spectroscopy experiments by using synchrotron radiation and compared the results with the theoretical spectra calculated within Density Functional Theory. The dominant role of the NbO6 octahedra in the formation of the energy spectra of KNbO3compound was demonstrated. The anomalous behavior of plasmons in ferroelectrics was exhibited by the function representing the characteristic energy loss in the region of phase transition. © 2014 Copyright Taylor & Francis Group, LLC.