We have recently developed an optical spectroscopy technique to monitor light scattering changes of the nervous system in vivo. Near infrared (NIR) spectroscopy emphasizes the detection of light scattering properties, which are prominent within the wavelength range of 700 to 850 nm wavelength. The purpose of this study is to test the hypothesis that demyelination and degeneration of the sciatic nerves after nerve injury will lead to a change in light scattering properties and be detected by the NIR technique. Left spinal nerve ligations (L4, L4 and L5, L5) were performed in rats. The scattering properties of the left (ligated) and right (control) sciatic nerve were measured by the NIR reflectance using a bifurcated needle probe at postoperative days 1, 4, 7, and 14. The results show that there was no significant difference among three types of ligation, and neither did the readings between left and right sciatic nerve at postoperative day 1. Significant decreases in light scattering indexes were found between left and right sciatic nerves at postoperative days 4, 7, and 14. It is concluded that our initial hypothesis is proven, suggesting that the NIR technique may have a potential for clinical application in detecting demyelination and degeneration of the nervous system.