The dependence of the impedance of the electrode double layer of mercury electrode on frequency around the potentials of the tensammetric peaks of single-stranded and double-helical polynucleotides and DNA was studied. from the frequency dependence of the impedance of the electrode double layer represented in a complex plane impedance plot (Nyquist plot, Cole-Cole plot), the electric equivalent circuit of the electrode covered with adsorbed DNA layer was determined. It was concluded that the desorption of ssDNA (single stranded, denatured) is accompanied by higher dielectric losses than the desorption of dsDNA (double stranded, native). This can be explained by the higher flexibilioty of ssDNA compared to the dsDNA. The capacitance peak of single stranded polyadenylic acid observed at pH 8 around -1.3 V splits at lopw frequencies in two peaks.