This paper presents a method to improve thermal conductivity using poly(methyl methacrylate)(PMMA), polystyrene(PS) blends, and incorporation of multiwalled carbon nanotubes (MWCNTs). MWCNTs are favorablly localized in PMMA phase to enhance thermal conductivity. In addition, Surface of MWCNTs was treated with PMMA to improve affinity between matrix and filler. PMMA grafting contribute to enhance filler localization on matrix phase. Composites using two polymers improved thermal conductivity by ~11% compared with composites using only PS or PMMA. Also, PMMA grafting on the surface of MWCNTs improved thermal conductivity by ~13% compared with samples without PMMA grafting.