The strain and/or stress shifts in the characteristic spectral peaks of natural cellulosic fibers are presented. The fibers were observed under the microscope of a Raman spectroscope. The method is capable of giving measurement of not only the degree of cell-wall damage, but also a means of calibrating the strain relative to the number of defects in a fiber. Stress concentration shows up as a bright region in the matrix material surrounding a defect in the fiber. The defects were found to promote brittle fracture of the material as a whole.