This study was carried out to identify the effect of oxidative stress on the pathogenesis of manganese intoxication. Five rats in experimental group were given with $MnCl_2$intraperitoneally for 4 weeks(4 mg/kg once daily 5 days per week) and another five rats for control group were given with normal saline. In experimental group, manganese concentrations increased significantly in nucleus accumbens by 142% (p<0.05), SOD activities increased significantly by 124%(p<0.01), and MDA concentrations increased significantly 148%(p<0.05) compared with control group. Among fatty acids, total n-6 polyunsaturated fatty acids(PU) increased significantly by 231%(p<0.05) compared with control group. Arachidonic acids(AA) increased by 224%(p<0.05), and these increase were composed mostly of n-6 polyunsaturated fatty acids(PUFA). Among n-3 PUFAs except linolenic acids, eicosapentanolc acid(EPA) decreased significantly by 38%(p 0.01) and docosahexanoic acids(DHA) decreased by 30% p<0.05) compared with control group. Our results suggest that the oxygen free radicals produced by manganese may cause compositional changes of fBtty acids in nucleus accumbens of the rat. Characteristics of fatty acids compositional changes by manganese were the decrease of EPAs and DHAs(n-3 PUFAs), and increase of AAs(n-6 PUFAs). These changes with the increase of MDA, suggest that manganese neurotokxcity is caused by lipid perokidation mediated with oxygen free radicals, especially superoxide radicals.