Effective　surface　modification　of　multi-walled　carbon　nanotubes　(MWCNTs)　by　covering　with　oleic　acid　was　carried　out　via　the　covalent　interaction　between　the　hydroxymethylated　MWCNTs　and　the　organic　long-chained　molecules　of　oleic　acid　in　xylene.　The　oleic　acid　modified　MWCNTs　were　characterized　through　FT-IR　spectroscopy,　X-ray　photoelectron　spectrometer,　transmission　electron　microscope,　thermogravimetry　and　dispersion　test　to　confirm　that　the　well　dispersed,　robust　and　functional　oleic　acid　had　been　introduced　on　the　surface　of　the　pristine　MWCNTs　without　sacrificing　the　original　morphological　structure　obviously.　Additionally,　the　nanocomposites　consisting　of　oleic　acid　modified　MWCNTs　and　a　polystyrene　(PS)　matrix　were　fabricated　by　solution　blending　method.　The　structure　and　morphology　of　the　oleic　acid　modified　MWCNTs/PS　nanocompsites　were　characterized　through　X-ray　diffraction　and　scanning　electron　microscopy　(SEM).　The　SEM　images　showed　that　the　functionalized　MWCNTs　had　a　very　well　dispersion　in　the　matrix.　Moreover,　the　thermal　stability　and　electronic　conductivity　presented　improvements　with　the　filler　concentration　increased.　Meanwhile,　the　nanocomposites　possessed　a　high　dielectric　constant　with　a　comparatively　low　dielectric　loss　before　the　MWCNTs　concentration　up　to　1.5　wt%.