The utilization of catechol as an electrochemical indicator in the presence of N-Acetyl-l-cysteine (NAC) at a carbon paste electrode (CPE) has been investigated in aqueous media using cyclic voltammetry (CV), differential pulse voltammetry (DPV), and double-step potential chronoamperometry methods. The results show that NAC participates in Michael type addition reaction with electrogenerated quinone from electrooxidation of catechol at CPE to form the corresponding thioquinone derivative. The reoxidation of the adduct leads to increase in the oxidative current which is proportional to the concentration of NAC. Therefore, in the optimum condition (pH = 6.00) by CV, the oxidation of NAC occurs at a potential about 400 mV versus Ag|AgCl|KClsat in the presence of catechol at the surface of CPE. The practical utility of the method showed that low detection limit and high sensitivity for voltammetric determination of NAC. The proposed method is useful for the routine analysis of NAC in pharmaceutical formulations.