A selective and highly sensitive electrochemical method, based on a poly(brilliant cresyl blue)-modified activated glassy carbon electrode, was developed for the simultaneous determination of hydroquinone (HQ) and catechol (CT). The modified electrode was characterized by cyclic voltammetry (CV). It was found that the modified electrode showed an excellent catalytic activity and enhanced reversibility toward the oxidation of both HQ and CT in 0.1 M phosphate buffer solution (PBS, pH 7.0). The peak-to-peak separations (Delta E-p) between oxidation and reduction waves in CV were decreased significantly from 360, and 285 mV at the bare electrode, to 59 and 56 mV at the poly(brilliant cresyl blue) modified electrode for HQ and CT respectively. Furthermore, the redox responses from the mixture of HQ and CT were easily resolved in both CV and differential pulse voltammetry (DPV). The oxidation peak currents of HQ and CT were linear up to 250 mu M with the detection limits (S/N = 3) of 60 and 56 nM for HQ and CT, respectively. The developed sensor was successfully examined for real sample analysis with tap water and it showed a stable and reliable recovery data with high reproducibility. (C) 2013 The Electrochemical Society. [DOI: 10.1149/2.008304jes] All rights reserved.