Effects of oxygen on the growth of carbon nanotubes (CNTs) using plasma-enhanced chemical vapor deposition (PECVD) have been studied. Oxygen gas was added to the CH4/H-2 atmosphere in the CNTs growth process and produces a large number of OH radicals. It is found that OH radical has a strong etching effect on CNTs, and a small amount of OH radical can efficiently purify CNTs and improve the activity of catalyst, thereby OH radical is benefit to the synthesis of high-quality and aligned CNTs array. Contrarily, the surface structure of CNTs can be etched and damaged when OH radical content is high, and the growth of CNTs is suppressed. It is expected that the method provided in the present study is useful for the synthesis of high-quality aligned CNTs array, and purification, modification and functionalization of the CNTs. (C) 2013 Elsevier Ltd. All rights reserved.