A novel poly(bromocresol green) (PBG)/carbon quantum dots (CQDs) composite based sensor was successfully fabricated on glassy carbon electrode by electropolymerization. As-prepared PBG/CQDs modified electrode was successfully applied in the simultaneous determination of guanine and adenine. Electrochemical responses of as prepared modified electrode were evaluated by cyclic voltammetry and differential pulse voltammetry. Owing to the synergistic effect of PBG and CQDs, the oxidation peaks of both guanine and adenine well separated from each other and the peak potential separation was large up to 310 mV. The current of the oxidation peaks showed a linear dependence on the concentrations of guanine and adenine in the range of 0.50-142 and 0.30-130 mu M with detection limits of 0.016 and 0.026 mu M (S/N = 3), respectively. Moreover, as-prepared PBG/CQDs modified electrode exhibited favorable selectivity, stability and reproducibility, which had promising application for the simultaneous determination of guanine and adenine.