The bioelectrocatalysis of cellobiose and lactose was studied at graphite electrodes modified with adsorbed cellobiose dehydrogenase (CDH) from Phanerochaete chrysosporium. At a low concentration of substrate, there was an optimum in the bioelectrocatalytic current around pH 4.7, whereas at high substrate concentrations, the catalytic current was decreasing continuously with increasing pH. An increase of the ionic strength of the buffer solution by the addition of 80 mM of NaCl resulted in a 50% increase of the catalytic current. Slow sweep cyclic voltammograms were used to extract the formal potential of the heme domain of the enzyme in the presence of the substrate, cellobiose, at different pH values. The formal potential of the heme decreased with increasing pH. Based on the results in this work, it was confirmed that there was a direct, non-mediated, electron transfer between the heme of CDH and the graphite electrode. Experimental results revealed that the enzyme was bound strongly to the surface of the graphite electrode and that this graphite-enzyme interaction did not result in denatured or a strongly changed structure of the heme domain of CDH on the electrode surface. The mechanism of the bioelectrocatalysis at graphite electrodes modified with CDH is discussed, focusing on the rate limiting steps of the electrocatalytic process.