As for the charge-transfer complex (CTC) formed by N-butyl maleimide (NMBI) and styrene in chloroform, the complex formation constant was determined by H-1-NMR of Hanna-Ashbaugh. The copolymerization of NBMI (NBMI, M-1) and styrene (St, M-2) in chloroform using AIBN as an initiator was investigated. On the basis of the kinetic model proposed by Shan, the reactivity ratios of free monomers and CTC in the copolymerization were calculated to be r(12) = 0.0440, r(21) = 0.0349, r(1C) = 0.00688, r(2C) = 0.00476, and the ratios of rate constants were obtained to be k(1C)/k(12) = 6.40, k(2C)/k(21) = 7.33. In addition, the copolymer was characterized by IR, H-1-NMR, DSC, and TGA.