We present an experimental study of contribution of charged domain walls into dielectric permittivity of lithium niobate. It has been shown that formation of dense structure with spike-like domains leads to order of magnitude increase of permittivity, which gradually decreases with time. The decrease rate accelerates under DC bias. Dielectric permittivity decreases linearly with a logarithm of frequency. The obtained results were explained considering vibration of the steps on the charged domain walls.