Objective:To study the protective effect of extracts of Ginkgo Biloba 761(EGb761)on injured motor neurons following brachial root avulsion.Methods:The nerve roots(C5-T1)of right brachial plexus of male a- dult Sprague Dawley rats were isolated and avulsed under the microscope;The injured rats were randomly divided into normal saline,EGb761 100 mg/kg·d treated and sham groups.The injured rats were intraperitoneally in- jected with 1ml normal saline or 100 mg/kg aqueous solution every day.After 6 and 8 weeks,all rats were killed and tbe ultra structure of injured C7 spinal segments were observed by transmission electron microscope.Results: In normal saline group,the bodies of motor neurons were shrunk.The nuclear chromatin curdled at the edge of nuclear membrane was splitting,divergent but the nuclear membrane was integrated.The amount of rough endo- plasmic reticula and the free ribosomes were decreased.Mitochondria and its spines were all swollen.The lamel- lar appearance of myelin sheath disappeared and became vacuolar.In EGb761 treated groups,there was less cur- dled nuclear chromatin.The cell membranes of injured motor neurons were also integrated but without shrunk nuclear membranes.The amount of rough endoplasmic reticula and the free ribosome were more than that in nor- mal saline group.The shape of mitocbondria and its spines remained normal.The lamellar appearance of myelin sheatb was clear and complete.Conclusion:EGb761 is effective in preventing some subcellular organelles deterio- ration in root avulsion-induced spinal motor neuron neuropathy.