This study describes a new approach for the investigation of electrocatalytic oxidation of sulfide using a pencil graphite electrode modified with quercetin (PGE/QH₂). Adsorption procedure was used for the preparation of the modified electrodes. It was observed that PGE/QH₂ showed a significant electrocatalytic activity toward sulfide oxidation. Cyclic voltammetric studies show that the peak potential of sulfide shifts from +450mV at bare PGE to +280mV at PGE/QH₂. The electrocatalytic currents obtained from amperometric measurements at +300mV vs. Ag/AgCl/KCl_sat and at pH 8.0 BR buffer solution containing 0.1M NH₄Cl were linearly related to the concentration of sulfide. The calibration graph consisted of two linear segments of 1–20μM and 20–800μM with a detection limit of 0.3μM (based on 3s_b). The proposed method was successfully applied to the determination of sulfide in waste waters and was compared with the spectrophotometric method.