The synthesis of copolymers between lignin from steam-exploded straw and 1-ethenylbenzene is described. Beforehand, lignin from steam-exploded straw was fully characterized by using elemental analysis, ultraviolet spectroscopy, gel permeation chromatography (GPC), Fourier transform infrared (FTIR), and both H-1 and C-13 nuclear magnetic resonance (NMR) spectroscopy. Using a previously described procedure utilizing calcium chloride and hydrogen peroxide as reagents the synthesis of the copolymers was performed. FTIR of the copolymers showed the presence of both lignin and polystyrene. GPC analysis showed the presence of a fraction with high molecular weights. These results were confirmed from both viscosity data and differential calorimetry.