An electrochemical sensor was fabricated and used to simultaneously determine guanine and adenine in DNA. In this work, the poly (2,6-pyridinedicarboxylic acid)/chemically reduced graphene oxide modified glass electrode (PPDA/CRGO/GCE) was constructed. The PPDA/CRGO/GCE was characterized by scanning electron microscopy. The modified electrode displayed greatly improved voltammetric response to guanine (G) and adenine (A). Differential pulse voltammetry (DPV) was used for individual or simultaneous determination of guanine and adenine. The electrode showed good reproducibility with linear ranges of 0.05-4.5 mu M and 0.1-6.0 mu M, detection limits of 0.01 mu M and 0.02 mu M for guanine and adenine, respectively. The electrochemical method for the measurement of guanine and adenine in calf thymus DNA was also developed and the result was satisfactory. (C) 2013 Elsevier B.V. All rights reserved.