Niacinamide was electropolymerised on the surface of glassy carbon electrode (GCE) by cyclic voltammetric technique (CV). The fabricated poly(niacinamide) modified glassy carbon electrode (MGCE) was used for the voltammetric determination of catechol (CC) and hydroquinone (HQ) in 0.2 M phosphate buffer solution (PBS) at pH 7.4 CV and differential pulse voltammetric (DPV) techniques. The study of concentration variation for both CC and HQ was conducted; the lower limit of detection was calculated to be 0.31 pM and 0.24 pM for CC and HQ by CV technique. The simultaneous separation of the analytes in a binary mixture was showed by the fabricated poly(niacinamide) MGCE by both CV and DPV techniques. The variation of applied scan rate on the binary mixture of CC and HQ was conducted and the results suggest the electrode process was diffusion controlled. The fouling effect by the adsorption of an oxidised product was eliminated by the modified electrode.