A simple and highly sensitive electrochemical method for the simultaneous and quantitative determination of catechol (CC) and hydroquinone (HQ) were developed based on the poly (Naphthol green B) modified carbon paste electrode. The modified electrode showed outstanding electrocatalytic activity and reversibility towards the oxidation of two phenolic isomers of Catechol (CC) and Hydroquinone (HQ) were performed at poly (NG B) MCPE by cyclic voltammetry in 0.2 M phosphate buffer solution of pH 7.4 at sweep rate 100 mV/s. Several factors affecting the electrochemical parameters, like the effect of sweep rate, pH and different concentration of both CC and HQ were studied. The simulations determination of CC and HQ in their sample mixture was analysed by using the cyclic voltammetric technique. The differences of the oxidation peak potentials for CC-HQ were about 0.124 V in cyclic voltammetry at 100 mV/s respectively. The interference studies showed that the modified electrode exhibits excellent selectivity. The detection limits were 0.19 and 0.20 mu M (20 to 90 mu M) for CC and HQ, respectively. Finally, this method can be used in the development of a sensor for sensitive determination of CC and HQ.