A technology of swelling and suspension copolymerization was conducted to graft styrene onto linear low-density polyethylene (LLDPE). The graft mechanism of styrene with LLDPE had been described by H-1 NMR and IR. The mean particle diameter and size distribution of the products with different proportions of LLDPE to styrene monomer were calculated. The morphology and thermal behavior of copolymers were characterized by scanning electron microscopy and differential scanning calorimetry. The glass transition temperature of copolymers increased with the addition of LLDPE, which proved the existence of the polyethylene-g-polystyrene copolymer. The grafting efficiency and granulation rate of suspension copolymerization were investigated. It was found that the grafting efficiency increased and the granulation rate decreased with the addition of LLDPE. POLYM. ENG. SCI., 50:1713-1720, 2010. (C) 2010 Society of Plastics Engineers