We have systematically measured the differential stress-optic coefficient, $\mathrm{\Delta }C$ , in a number of poly(methyl methacrylate) (PMMA) fibers drawn with different stress, ranging from 2 up to $27\mathrm{MPa}$ . $\mathrm{\Delta }C$ was determined in transverse illumination by measuring the dependence of birefringence on additional axial stress applied to the fiber. Our results show that $\mathrm{\Delta }C$ in PMMA fibers has a negative sign and ranges from $-4.5$ to $-4.5\times {10}^{-12}{\mathrm{Pa}}^{-1}$ , depending on the drawing stress. Increase of the drawing stress results in greater initial fiber birefringence and lower $\mathrm{\Delta }C$ .