The copolymerization of styrene (St) and acrylonitrile (AN) complexed with CuCl2 monomer by a free radical mechanism was performed using benzoyl peroxide as an initiator at 65℃ under N2 atmosphere for 150 min. The rate of polymerization (Rp) was found to increase linearly with the concentration (in mol/L) of CuCl2, AN and St through scaling relations. The activation energy of the copolymerization process in the presence and absence of CuCl2 was found to be 46.5 kJ/mol and 102 kJ/mol, respectively. The viscosity average molecular weight of the copolymer and the kp2/kt ratio were determired to further assess the accelerating effect of CuCl2 on the copolymerization process. The copolymerization process in the presence of CuCl2 has a radical complex mechanism.