An optomechanical characterization was carried out to investigate the influence of grafting polyamide-6 fibers with poly (methyl methacrylate) (PMMA) on their structural relationship properties. Intrinsic optical properties of the modified sample were determined using a method based on the cold drawing process. The Mach-Zehnder interferometer attached with mechanical drawing device was used to determine the refractive indices and birefringence of the polyamide-6 samples at different draw ratios. A graphical method was used to determine the intrinsic birefringence of modified polyamide-6 with PMMA and it was found to be 0.0673 which is less than pure polyamide-6. The resulting data was used to estimate some structural parameters such as the orientation function, optical orientation angle and structural constant. The drawing effect is more significant on the modified sample than on the pure sample. It was found that the grafting process produced a material with new properties that can be used in different applications.