Thermally conductive polystyrene (PS)/multi-walled carbon nanotubes (MWNTs) nanocomposites was prepared through a simple solution-evaporation method assisted by ultrasonic irradiation. To enhance the dispersion of MWNTs in PS, MWNTs were chemically functionalized with poly(styrene-co-maleic anhydride) (SMA) (MWNT-g-SMA), which had benzene group and exhibited strong affinity with PS. The thermal conductive properties of PS increased and the mechanical properties decreased in presence of MWNTs, while by addition of MWNT-g-SMA, the properties of the composites can be improved to some extent. The thermal conductivity can reach 0.89 W/m K for the composite with 33.3 vol % MWNT-g-SMA, which was four times higher than that of neat PS. A linear increase of the thermal conductivity was observed with increasing MWNTs-g-SMA content, and the Maxwell-Eucken model and the Agari model were used for theoretical evaluation. Compared with MWNT-OH, MWNT-g-SMA with larger diameter exhibited diffused boundary with the PS matrix, resulting from the strong interfacial bonding of the two phases. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 116: 2336-2342, 2010