An electrochemical sensor was fabricated and used to simultaneously detect guanine and adenine. In this study, nano-copper oxide-modified glassy carbon electrode (nano-copper oxide/GCE) was prepared by electrodeposition. The nano-copper oxide/GCE was characterized by electrochemical impedance spectroscopy and scanning electron microscopy. The fabricated nano-copper oxide/GCE sensor exhibited sensitive response to guanine and adenine in 0.1 M PBS (pH 7.0). The anodic peak currents were linear with the guanine and adenine concentrations over the range of 0.05-1.2 mu M with the correlation coefficients of 0.9997 and 0.9993, respectively, and the corresponding detection limits were 6 x 10(-3) mu M and 9 x 10(-3) mu M (S/N = 3), respectively. The nano-copper oxide/GCE could be applied to simultaneously detect guanine and adenine in samples with good anti-interference ability.