1,10-Phenanthroline-5,6-dione and glucose oxidase modified and unmodified graphite rod electrodes (GRE) were investigated in buffer with 0.04 mol, L-1 of glucose by electrochemical impedance spectroscopy (EIS). The EIS was conducted under potentiostatic conditions and showed relatively good stability. The impedimetric results were evaluated using estimated equivalent circuit. The EIS based study demonstrated redox mediating properties of 1,10-phenanthroline-5,6- dione deposited on GRE. EIS characteristics observed in this study show that electrodes modified by both 1,10-phenanthroline-5,6-dione and glucose oxidase can be used as an impedimetric glucose biosensor. © 2013 The Electrochemical Society. All rights reserved.