[en] The results of elastic and inelastic neutron scattering studies on the phase transition and vibrational spectra in CsHSeO₄ superionic conductor at the IBR-2 pulsed reactor are reported. The characteristic features of the phase transition are discussed in comparison with the data obtained earlier on CsHSO₄ superionic conductor. From the experimental data the conclusion has been drawn that the protons are partially disordered and this process is accompanied by structural changes far below the transition temperature. The disordering process is an activation one. The high temperature phase is metastable and the obtained neutron diffraction spectra cannot be explained by the unit cell parameters already proposed by other authors