For the purpose of studying the molecular mechanism of the traumatic brain injury, we have established a reproducible graded lateral fluid percussion model of experimental brain injury in the rat with a modified fluid percussion device. The device consists of a stainless steel cylindrical reservoir instead of the plexiglass reservoir, a steel reservoir filled with compressed gas instead of the pendulum for making more accurate percussion pressure, an apparatus for releasing the pressure immediately after the percussion, and a computer for recording and storing the percussion data. Pathologic examination demonstrated subdural hemorrhage, subarachnoid hemorrhage, and hemorrhage in the lateral ventricle and corpus callosum on the percussion side. The severity of pathologic changes increased with the magnitude of percussion. The results indicate that the new device could inflict reproducible graded lateral fluid percussion brain injury on rats and the model can be used for the studies of neuropathologic and molecular mechanism of brain injury.