This work studied oxygen plasma treatment, at different times, on vertically aligned multiwalled carbon nanotube (VACNT) surfaces using the pulsed-discharge plasma technique. As-grown VACNT surfaces were superhydrophobic. Pure oxygen plasma etching modified VACNT surfaces to get a superhydrophilic behavior after only 2 min. Contact angle and surface energy measurements by the sessile drop method examined the VACNT surface wetting. X-ray Photoelectron Spectroscopy showed the heavy grafting of oxygen-groups onto VACNT surfaces after oxygen plasma etching. The results showed the great influence of polar groups on wetting behavior, with a strong correlation between the polar part of the surface energy and the oxygen content on the VACNT surfaces. These findings proved that oxygen plasma etching is a rapid and efficient method for functionalization of VACNT surfaces.