Polyoxymethylene (POM)/multiwalled carbon nanotubes (MWNTs) nanocomposites were prepared through a simple solution-evaporation method assisted by ultrasonic irradiation. To enhance the dispersion of MWNTs in POM, MWNTs were chemically functionalized with PEG-substituted amine (MWNT-g-PEG), which exhibited strong affinity with POM due to their similar molecular structure. The thermal conductivity and the mechanical properties of the composites were investigated, which showed that the thermal conductive properties of POM were improved remarkably in the presence of MWNTs, whereas reduced by using MWNT-g-PEG due to the heat transport barrier of the grafted-PEG-substituted amine chain. A nonlinear increase of the thermal conductivity was observed with increasing MWNTs content, and the Maxwell-Eucken model and the Agari model were used for theoretical evaluation. The relatively high effective length factor of the composite predicted with mixture equation indicated that there were few entangles of MWNTs for the samples of MWNT-g-PEG in the composites. The mechanical strength of the composites can be improved remarkably by using suitable content of such functionalized MWNTs, and with the increase of the aliphatic chain length of PEG-substituted amine, the toughness of the composites can be enhanced. Transmission electron microscope result indicated that MWNT-g-PEG exhibited strong affinity with POM and a good dispersion of MWNTs was achieved in POM matrix. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 905-912, 2010