Abstract: Objective To observe effect of aluminum on the changes of number and structure of neurons in brain and granulovacuolar degeneration(GVD)in hippocampus in rats and to provide some evidences on the mechanism of neurotoxicity.Methods One hundred fourty four rats were divided into three experimental and control groups,experimental groups were given aluminum by intraperitoneal injection with aluminum chloride in 5.0,15.0 and 25.0mg/kg respectively.The change of number and structure of nerve cells were observed in different domain of brain with microscope and electron-microscope.Results 15.0mg/kg for 4 weeks or 5.0mg/kg for 12 weeks group could result in the decrease of neurons in cerebrum,Pukinje cells in cerebellum and pyramidal neurons in hippocampus significantly(P<0.05);the number of GVD cells increased significantly(P<0.05)when the dosages of aluminum at 5.0mg/kg for 8 weeks or 15mg/kg and 25mg/kg for 4 weeks;the incidence of GVD per 300 nerve cells were significantly related to the dosage of aluminum;Nissl bodies dissolving and dissipating,nucleus-shrinkage were observed by microscope at 5.0mg/kg for 8 weeks or 15.0mg/kg for 4 weeks;nucleus membrane transfigure and dissolving,micronucleus small,nucleus circumference vacant-spongy,mitochondria enlarging were detected with electronic-microscope;the swell and vacant-spongy of never cells nucleus of hippocampus at dosage of 15.0mg/kg for 12 weeks.Conclusion The results confirmed profoundly that aluminum had nerve toxicity and might play an important role in increasing the risk of GVD,and suggested that nerve toxicity might be related to the number decreasing and structure changing of neurons due to the dosage of aluminum.