In this report, a voltammetric sensor for simultaneous determination of hydroquinone (HQ) and catechol (CC) was developed at a glassy carbon electrode modified with graphene (GR/GCE). The separation of oxidation and reduction peak (Delta E) is decreased from 281 to 31 mV for HQ and from 250 to 26 mV for CC at GR/GCE, respectively. Separation of the oxidation peak potentials for HQ and C:C was about 112 mV in 0.10 M acetate buffer solution (pH 4.5), and the anodic currents for the oxidation of both HQ and CC are greatly increased at GR/GCE, which makes it suitable for simultaneous determination of these compounds. Under the optimized condition, the anodic peak current of HQ is linear with the concentration of HQ from 1 x 10(-6) to 5 x 10(-5) M in the presence of 5 x 10(-5) M CC. A detection limit of 1.5 x 10(-8) M (S/N = 3) can be achieved. At the same time, the anodic current of CC is linear with the concentration of CC from 1 x 10(-6) to 5 x 10(-5) M with a detection limit of 1.0 x 10(-8) M (S/N = 3) in the presence of 5 x 10(-5) M HQ. The proposed sensor was successfully applied to the simultaneous determination of HQ and CC in tap water, and the results are satisfactory. (C) 2010 Elsevier B.V. All rights reserved.