In order to monitoring the development of traumatic brain edema in vivo, a specifically designed optical parameters of tissue testing system wit h a mini-invasion bifurcated optical fiber probe and a fiber spectrometer was used to monitor the reduced scattering coefficient(μ′s) of t he rat traumatic brain while the counterpart parameter, i.e. brain water content (BWC), was also measured. Acute rat regional brain trauma was applied according to Feeney’s apparatus. The changes of brain edema were monitored by near-infrared spectroscopy (NIRS) technology and by measuring the water content of the brain. Experiment result showed that distinct brain edema in injured areas was found at 6 hours later after trauma, which reached a summit of severity at 24-72 hours later after trauma, then gradually declined. After using the dehydrant, the brain edema situation became better, and then, the edema occurred again whilet he medicamentosus effect of dehydrant was gradually lost. It can be showed that μ′s had similar change profile wit h BWC and the two parameters were well linearly relative to each other. μ′s is a good indicator for monitoring traumatic brain edema and t he medicamentosus effect of dehydrant. As a result near-infrared spectroscopy is a new feasible method of monitoring the development of traumatic brain edema in vivo.