1,10-Phenanthroline-5,6-dione and glucose oxidase modified and unmodified graphite electrodes were analysed in buffer/glucose media by the electrochemical impedance spectroscopy (EIS) method. The EIS analysis was carried out under potentiostatic conditions. The gathered impedimetric data was evaluated applying estimated equivalent circuits. It was determined that equivalent circuit R-Omega (R-F2 C-2)( C[RFW) most optimally describes this electrochemical system. The study revealed redox mediating properties of 1,10-phenanthroline-5,6-dione deposited on graphite electrodes. 2014 Elsevier Ltd. All rights reserved.