In recent years, much attention has been paid to graphene due to its high aspect ratio and remarkable electrical, thermal and mechanical properties, which make graphene a promising nanofiller for improving electrical, thermal and mechanical properties of polymers [1-4].This talk presents our recent progress on preparation and properties of polymer/graphene nanocomposites by in situ polymerization, and solution blending.(1) Electrically conductive and thermally stable polyamide 6/graphene oxide (GO) nanocomposites synthesized by in situ polymerization and thermal reduction.By dispersing the electrically insulating and thermally unstable GO nanosheets in ε-caprolactam monomer followed by in situ polymerization, the electrically conductive polyamide 6 nanocomposites were prepared, in which GO was thermally reduced during the polymerization process.The incorporation of GO greatly improved the electrical conductivity of polyamide 6 resulting in a sharp transition from electrical insulator to semiconductor with a low percolation threshold.(2) Functionalized GO with octadecylamine (GO-ODA) and its electrically conductive polystyrene nanocomposites Simultaneous surface functionalization and chemical reduction of GO was realized by simple refluxing of GC with octadecylamine (ODA) without the addition of any reducing agents.The presence of the long octadecyl chain made the hydrophilic GO hydrophobic.Interestingly, different from insulating GO, GO-ODA became electrically conductive due to the chemical reduction of ODA.The electrical conductivity of GO-ODA was further increased by thermal reduction during the compression-molding of its polystyrene nanocomposites, The high conductivity of the polystyrene/GO-ODA nanocomposites is attributed to the improved dispersion and the reduction of GO-ODA in comparison with GO.