Sulfasalazine (SSZ) is a pharmaceutical compound used for the treatment of rheumatoid arthritis. The electrochemical oxidation of SSZ at a glassy carbon electrode was studied by cyclic, differential pulse and square wave voltammetry in a wide pH range. For electrolytes with pH<11.0, the oxidation is an irreversible, diffusion-control, pH-dependent process that involves the transfer of one electron and one proton from the hydroxyl group of the salicylic moiety. For pH>11.0 the oxidation is pH-independent, and a pKa≈11 was determined. The formation of a quinone-like oxidation product that undergoes two electrons and two protons reversible redox reaction was observed. Also, UV-vis spectra of SSZ were recorded as a function of supporting electrolytes pH. An electrochemical oxidation mechanism was proposed.