Noncatalyzed and catalyzed electrochemical oxidations of multiwalled carbon nanotubes (CNTs) were studied with the aim to understand their durability as catalyst support in polymer electrolyte membrane (PEM) fuel cells. Bare and Pt-deposited CNTs were investigated in <mml:math display="inline"><mml:mrow><mml:mn>1.0</mml:mn><mml:mspace width="0.3em"></mml:mspace><mml:mi mathvariant="normal">M</mml:mi></mml:mrow></mml:math>1.0M sulfuric acid at a constant potential of <mml:math display="inline"><mml:mrow><mml:mn>1.2</mml:mn><mml:mspace width="0.3em"></mml:mspace><mml:mi mathvariant="normal">V</mml:mi></mml:mrow></mml:math>1.2V . Carbon black (CB, Vulcan XC-72R) was also studied under the same experimental conditions. The carbons were oxidized at room temperature in the form of thin-film electrodes with time durations up to <mml:math display="inline"><mml:mrow><mml:mn>48</mml:mn><mml:mspace width="0.3em"></mml:mspace><mml:mi mathvariant="normal">h</mml:mi></mml:mrow></mml:math>48h . Cyclic voltammetry was used to monitor the surface oxide redox reactions as a way to quantify the degree of surface oxidation on the carbons. It was found that the redox current peaks were stabilized after <mml:math display="inline"><mml:mrow><mml:mn>8</mml:mn><mml:mspace width="0.3em"></mml:mspace><mml:mi mathvariant="normal">h</mml:mi></mml:mrow></mml:math>8h for CNTs, but they continue to increase for CB, showing that CNTs are more resistant to electrochemical oxidation. Similar trends were observed in the catalyzed oxidation with Pt-deposited carbons. However, much larger currents were observed, demonstrating that catalyzed oxidation had indeed occurred. The observed durability demonstrated that CNTs would be a better catalyst support in PEM fuel cells in which the commonly used CB often undergoes severe electrochemical corrosion.