Abstract: In this article a series of high impact polystyrene/graphene (HIPS/Gr) nanocomposite were prepared by solution mixing method and their morphology, thermal and mechanical properties were investigated as a function of Grpahene content. SEM images and X-ray diffraction data confirm that the graphene platelets are well dispersed in HIPS matrix for the nanocomposites with Gr contents up to 4.0 wt%. Mechanical properties analysis demonstrate that yielding strength and initial modulus of HIPS/Gr nanocomposite are highly improved with the increment of Gr content compared to pure HIPS. The nanocomposites exhibited noticeable improvement in thermal stability compared to pure HIPS. Keywords: Nanocomposite, Graphene, Mechanical Properties, Morphology