Three kinds of modified multiwalled carbon nanotubes (MWNTs) with different length were obtained by grafting carboxylic groups on long MWNTs or copolymer groups on short and long MWNTs. The modified MWNTs were examined by infrared spectroscopy, thermal gravimetric analysis, X-ray photoelectron spectroscopy, and field emission scanning electron microscopy (FESEM). Afterward, the modified MWNTs were introduced into poly (furfuryl alcohol) (PFA), and the tribological behaviors of the resultant PFA composite coatings were investigated using a ring-on-block wear tester under dry friction condition. The dispersion of MWNTs in PFA composites and the worn surfaces were investigated by FESEM. The results indicated that the MWNTs dispersion and the tribological behaviors of PFA composite coatings could be obviously improved by modification with the copolymer. More significantly, under similarly uniform dispersion of MWNTs, the tribological properties of PFA composite coatings with short nanotubes presented better results when compared with those with long nanotubes because of the influence of nanotube length on the degree of modification of the MWNTs surfaces. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 118: 2881-2889, 2010