The purpose of this study is to investigate the composition and structural changes of aspen and fir barks for thermochemical transformation and to determine the electrical capacity of the obtained carbonized barks. Significant differences of the structural and current-voltage characteristics of carbonized barks were revealed. The carbonized product from aspen bark mainly consists of the amorphous carbon and the crystalline phase of calcium hydroxide; the product from fir bark consists of amorphous-crystalline carbon.Cyclic voltammetric curves indicate the formation of electric double layer in the obtained carbon products and imply their potential use for energy accumulation and storage. Passing of Faraday processes and the pseudo-capacity are revealed in aspen carbonized at 800 °C. These features are absent in the carbon product obtained from fir bark. The apparent specific capacity of carbonized aspen bark (450 Fg-1) is higher than carbonized fir bark (83 F*g−1).The probable reason is the effect of oxides of metal such as calcium, magnesium, potassium and sodium, which content is two times higher in the aspen bark compared to the fir bark. The apparent specific capacity as function of the potential sweep speed is different for aspen and fir barks. This difference can be caused by the inhomogeneous distribution of mineral substances in the carbon matrix.