A new method to functionalize multiwalled carbon nanotubes (MWNTs) with amphiphilic poly(aspartic acid) was investigated. The amphiphilic polymer (PASP-C16) was synthesized by thermal condensation and aminolysis by hexadecylamine, followed by hydrolysis of the remaining succinimide units in the polymer backbone. The functionalization of MWNTs was achieved by physical adsorption of the biopolymer onto the surfaces of MWNTs. Ultraviolet-visible (UV-vis) spectra showed that the functionalized MWNTs had a good aqueous dispersity and solubility. The interaction of PASP-C16 with MWNTs was investigated by analyzing X-ray diffraction (XRD) patterns, circular dichroism (CD), spectra and high-resolution transmission electron microscopy (HRTEM). From the XRD patterns, it can be known that the aggregate of PASP-C16 due to intermolecular interaction between hexadecyl chains has been reduced when the polymer interacting with MWNTs. CD spectra indicated that the interaction of hexadecyl chains of PASP-C16 with the wall of MWNTs is the major interaction between PASP-C16 and MWNTs, and MWNTs were covered by the poly(aspatic acid) backbone. (C) 2010 American Institute of Chemical Engineers AIChE J, 57: 772-777, 2011