This Letter proposes a novel chemo-mechanical method to in situ functionalize carbon nanotubes (CNTs). Ball milling in the presence of ammonium bicarbonate allowed the introduction of amine and amide groups onto the surface of CNTs, resulting in the conversion of the semiconducting behavior of CNTs from p-type to n-type. The corresponding electrical conductivity of CNT increased gradually with ball milling time, presenting a remarkable 250% increase after 9 h of milling. These interesting observations are attributed to the nitrogen compounds introduced on CNTs, which function as the electron donor in the material. (C) 2008 Elsevier B.V. All rights reserved.