The electrochemical cyclic voltammetric (CV) oxidation behavior of an arc-derived single-wall carbon nanotube (SWNT) sample in potassium hydroxide solution was investigated. Amorphous carbon in the as-grown SWNT sample was effectively removed by the CV oxidation, as confirmed by analyzing the sp3/sp2 carbon ratio from C1s XPS spectra and HRTEM observations. The removal of the amorphous carbon led to the exposure of metal nanoparticles, hence facilitating the elimination of the metal impurities by subsequent HCl washing. The CV oxidation can be applied as an alternative oxidative treatment for the purification of SWNT samples. Redox peaks were observed during the CV oxidation. The reduction peaks in the range of −0.96 to −1.0 V and the oxidation peaks in the range of −0.61 to −0.49 V were attributed to the electrochemical redox transformations between metallic Fe and Fe(II) oxide, Fe(II) oxide and Fe(III) oxide, as well as Ni and Ni(II) oxide, and the observed reduction peaks in the potential range of 0.29...