Rubber modified and unmodified poly(acrylonitrile/methyl acrylate) (75/25) copolymers [(Barex® resins) (Barex® is a registered trademark of Vistron Corporation, a subsidiary of The Standard Oil Company, Ohio)] were stretched at varying strain rates at different temperatures. Molecular orientation of the stretched samples at different extension ratios was determined using birefringence, the X-ray orientation factor, and infrared dichroism. The birefringence of rubber modified copolymers, which were prepared by graft copolymerization of the poly(acrylonitrile/methyl acrylate) copolymer with 10 parts (by weight) of a poly(butadiene/acrylonitrile) rubber, is found to be appreciably different as compared with the birefringence of unmodified poly(acrylonitrile/methyl acrylate) copolymer. The possible reasons for this difference are discussed. The orientation measured from the three techniques is compared, and the effects of temperature of stretching and of strain to are discussed. The maximum values of the birefringence of these two copolymers and that of the polyacrylonitrile have been estimated. Transition moment angles for CH2 and CN stretching bonds are obtained. From the birefringence data at various temperatures and strain rates, the activation energies of these two copolymers have been obtained.