A simple chemo-mechanical method is proposed for in-situ amino functionalization of carbon nanotubes (CNTs). Ball milling in the presence of ammonium bicarbonate (NH4HCO3) allowed introduction of functional groups like amine, amide on the surface of CNTs. The milled CNTs were characterized extensively using a particle size analyzer, a transmission electronic microscope, Raman spectrometry, X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry and surface area measurement to evaluate the influences of ball milling conditions. The results show that CNTs milled with NH4HCO3 were more effectively disentangled and shortened than those without the chemical. The amino termination of the functionalized CNTs makes it possible to covalently bond to polymers and biological systems, as well as the potential applications in electronics industry.