Abstract: Multiwalled carbon nanotubes (MWCNTs) were modified by grafting with hexamethylene diamine to obtain reactive amine groups. Acid treatment was used to shorten the MWCNTs by cutting at defect sites. Carboxyl groups produced by the acid treatment were converted to carbonyl chloride by thionyl chloride, and hexamethylene diamine was grafted to the ends of the cut MWCNTs by its substitutional reaction with carbonyl chloride. XPS, TEM and SEM were used to characterize the samples during the course of modification. Results indicated that MWCNTs were shortened from tens of microns to about 500 nm by the acid treatment. Hexamethylene diamine was successfully grafted onto the ends of the MWCNTs with a grafted N content as high as 3.29 mol %. The grafted MWCNTs can be dispersed uniformly in acetone.