Multiwalled carbon nanotubes (MWCNTs) were modified via polymerization of styrene under microwave irradiation, and polystyrene (PS)-MWCNT composites with individual-dispersed nanotubes were prepared by melt-mixing using industrial extruder and injection moulding machine. The microscopic morphologies of modified MWCNTs (m-MWCNTs) and composites were studied through transmission electronic microscopy and scanning electron microscopy. Result showed that a PS coat layer was introduced on the m-MWCNT surfaces, improving the compatibility of nanotubes with poor polar materials such as tetrahydrofuran, toluene, and PS matrix. Contrary to the composite prepared directly using purified MWCNTs (PS-p-MWCNT composite) without further modification, the composite prepared using m-MWCNTs (PS-m-MWCNT composite) exhibited a PS middle layer between nanotubes and matrix, leading to a strong interfacial adhesion. Thereby, although the nanotubes are individually dispersed in both PS-p-MWCNT and PS-m-MWCNT composites, the mechanical property of the latter is better than that of the former. When the nanotube content is 0.32 wt%, the PS-m-MWCNT composite had a 250% increase of impact strength as compared to pure PS, but the PS-p-MWCNT composite had only a 150% increase. Furthermore, the tensile strength of PS-p-MWCNT composite descended slightly with the addition of nanotube content, whereas, that of the PS-m-MWCNT composite ascended slightly. (C) 2009 Elsevier Ltd. All rights reserved.