A facile noncovalent approach is proposed to graft phosphonate groups onto the surface of the multiwall carbon nanotubes (MWCNTs) by pi-pi stacking interaction between naphthalen-1-ylmethylphosphonic acid (NYPA) and MWCNTs. Noncovalently attachment of phosphonate groups on the MWCNTs surface is confirmed by Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and zeta potential analysis. The water-soluble phosphonate functionalized MWCNTs are further deposited with Pd nanoparticles (Pd-NPs) as electrocatalyst for formic acid oxidation. The morphology and structure of Pd-MWCNTs nanocomposites are characterized by transmission electron microscopy (TEM). X-ray diffraction (XRD) and XPS measurements. It is observed that Pd-NPs are highly dispersed and effectively anchored on the side walls of the phosphonate functionalized MWCNTs. The Pd-MWCNTs nanocomposites exhibit better electrocatalytic activity and long-term stability for formic acid electrooxidation than the un-phosphonated counterpart. (C) 2012 Elsevier B.V. All rights reserved.