The copolymerization of ethyl methacrylate [I] with N-(3-chlorophenyl)maleimide [II], N-(4-chlorophenyl)maleimide [III], N-(3-bromophenyl)maleimide [IV], and N-(4-bromophenyl)maleimide [V] was carried out in benzene, using alpha,alpha＇-azobisisobutyronitryle as an initiator at 60 degrees C. The copolymer compositions were estimated by elemental analysis. The monomer reactivity ratios of [I] (r(1)) with [II], [III], [IV], and [V] (r(2)) were determined by the Fineman-Ross and Kelen-Tudos methods, and recalculated using the nonlinear minimization algorithm based on Mayo-Lewis＇s method (RREVM). The Alfrey-Price copolymerization parameters Q and e for N-(3-or 4-halogenphenyl)maleimides were also calculated. The kind of halogen atom (Br- or Cl-) and its position in the phenyl ring of maleimide on the values of reactivity ratios r(1) and r(2) are discussed.