A strong acidic solution is generally beneficial to both the electrochemical oxidation of the conducting polymer monomers and the regular growth of their corresponding polymers using cyclic voltammetry. Here, poly(Nmethylthionine) (PNMTh) is prepared at a reduced graphene oxide (rGO) electrode in a strong acid solution using electrochemical polymerization, and the PNMTh/rGO nanocomposite acts as a novel electrochemical sensing material for highly sensitive detection of hydroquinone (HQ). Structures and properties of the obtained nanocomposite are characterized via scanning electron microscopy (SEM), Fourier transform infrared spectrometry (FTIR), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV). Owing to the synergistic effect between PNMTh (redox properties) and rGO (large specific surface area and high conductivity), the PNMTh/rGO nanocomposite effectively enhances the electron transfer between HQ and the electrode, and thus reduces the overpotential of HQ oxidation. A linear regression area from 1.0 to 1000.0 mu M and a detection limit with 0.75& #x202F;mu M are obtained. More importantly, catechol does not interfere with the determination of HQ. These results demonstrate that the new PNMTh/rGO nanocomposite has great potential applications in electrochemical sensors and other electronic devices.