A quantitative method for detection of bisphenol A (BPA) was set up based on a glassy carbon electrode (GCE) modified with Ag nanoparticles and polyguanine (Ag-PGA). Under the optimum conditions, this modified electrode could remarkably enhance the electrochemical oxidation peak current of BPA, which made this method had wider linear range from 1.0 × 10–8 to 1.0 × 10–4 M, and lower limit of detection of 1.0 × 10–9 M (S/N=3). Moreover, this method has been successfully applied for the determination of BPA in real samples with satisfactory recovery.