Glutathione is a sulfur-containing molecule very interesting to study because it is related to several diseases. Also, it is an electroactive compound, but direct electrochemical studies are complex due to surface electrode passivation, which can be resolved by using modified electrodes. In this work, an electrode based on naphthoquinone (NQ) in a glassy carbon (GC) electrode modified with multi-walled carbon nanotubes (GC/MWCNT@NQ) has been prepared to study the reaction of NQ toward glutathione (GSH) in aqueous medium. A GC electrode was modified with MWCNTs using the drop-casting technique to obtain a GC/MWCNT electrode and subsequently was immersed in a 0.1 mM NQ solution to produce a GC/MWCNT@NQ electrode. The reaction of NQ toward GSH yields an NQ-GSH adduct, which is isolated in GC/MWCNT@NQ-GSH electrode, and shows the same electrochemical behavior as the GC/MWCNT@NQ electrode in phosphate-buffered saline, PBS, at pH 7.44 and, this reaction shows chemical reversibility when the cell contains GSH. The addition of GSH was followed by differential pulse voltammetry technique, showing a good linear tendency, and decreasing in 5% the initial peak current of NQ at 4.98 mu M of GSH