A novel voltammetric sensor was developed based on glassy carbon electrode (GCE) modified with a thin film of multiwalled carbon nanotubes (MWCNTs) coated with an electropolymerized layer of L-arginine. The resulting electrode was applied for simultaneous determination of Hydroquinone (HQ) and catechol (CC). The surface morphology and property of the modified electrode were characterized by scanning electron microscopy and electrochemical impedance spectroscopy techniques. Bare GCE fails to resolve the voltammetric signals of HQ and CC in a mixture. However, the modified electrode not only separates the voltammetric signals of HQ and CC, but also shows higher oxidation current for these molecules. CV and DPV results showed that the isomers can be detected selectively and sensitively at modified glassy carbon electrode with peak-to-peak separation about 111 mV. Under the optimized condition, the detection limits of CC and HQ are 40 and 62 nM (S/N = 3). The present electrode was applied to the simultaneous determination of HQ and CC in rain and tap water samples, which make it a promising candidate for designing an effective dihydroxybenzene sensor. (C) 2016 The Electrochemical Society. All rights reserved.