The electrochemical behavior of adenine at a glassy carbon electrode (GCE) modified with a nanocomposite consisting of graphene oxide and polyaniline was investigated by cyclic voltammetry and differential pulse voltammetry. The nanocomposite was synthesized by polymerization and characterized by Raman and UV-vis spectroscopy, and its morphology was examined by scanning electron microscopy. Adenine is oxidized at the modified GCE at a working potential of 1.2 V (vs. Ag/AgCl) and gives a current density of approximately 2.64 nA.cm−2, which is distinctly increased compared to the 0.57 nA.cm−2 of a bare electrode. Peak current and adenine concentration are linearly related to each other in the range from 0.5 μM to 20 μM. The modified GCE exhibits acceptable analytical performance, with a detection limit of 72 nM and a limit of quantification of 240 nM. It is excellently reproducible, stable, and fabrication is simple.