This study sheds light on the changes produced by the effects of cold-drawn fibers on the microstructure and macrostructure of viscose fibers. The optical properties and strain produced in viscose fibers were measured interferometrically at room temperature. Structural parameters were calculated, Such as the work per unit of volume, the reduction in entropy due to elongation, and the harmonic mean specific refractivity. In addition, the resulting data were used to calculate the optical stress coefficient and optical configuration and to apply the Mooney-Rivlin equation to determine the constants. Also, the number of crystals per unit Of Volume and the average orientation angle for uniaxial stretching were calculated with the extension ratios. The relation between the true stress and strain hardening was calculated. The average value of the maximum birefringence was determined to equal 0.046. The relations between the optical and mechanical changes with different parameters were established for the studied fibers. Microinterferograms and curves were drawn for illustration. (c) 2008 Wiley Periodicals, Inc.