A water soluble chitosan derivative (p-chitosan) was synthesized and used to functionalize multiwalled carbon nanotubes (MWCNTs) through the noncovalent interaction. The interaction of p-chitosan with MWCNTs was investigated by analyzing the spectra of ultraviolet-visible, Fourier transform infrared, Raman, and X-ray photoelectron. Circular dichroism spectroscopy was used to study the interaction as well. The results of the circular dichroism spectra indicate that, the interaction of p-chitosan with MWCNT makes p-chitosan less regularly structured. It was found that the interaction of p-chitosan with MWCNTs at a lower temperature is stronger than that at a higher temperature; pH conditions affect the interaction between p-chitosan and MWCNTs. (C) 2011 American Institute of Chemical Engineers AIChE J, 58: 285-291, 2012