Objective To observe the effects of iodine excess on expressions of neuron specific enolase(NSE) and glial fibrillary acidic protein(GFAP) in filial generation of rats.Methods The Wistar rats were divided into five groups by randomized design.The rats were drinking water at different iodine levels(NI,5HI,10HI,50HI and100HI).After being fed three months,the rats were mated and their filial generations at the age of 60 day observed.The serum thyroid hormones at the age of 60 day were measured.Immunohistochemical method combining with image analysis techniques were used to demonstrated expressions of NSE and GFAP in hippocampus of both control and iodine excess rats.Results The results of serum thyroid hormones revealed the decreasing tendency in experimental groups by gradually increasing iodine intake,however,hypothyroidism were obviously in 100HI group.Immunohistochemical staining and morphological images analysis of NSE positive neurons in hippocampus CA3 area indicated that numerical density on area(N-A),volume density(V-V) and the average of grey scale were gradually decreased coincidenced with iodine excess levels,furthermore,statistically significance in 100HI group.GFAP positive astrocytes in hippocampus CA3 area showed that the changes of the astrocytes were insignificant.Conclusions NSE expressions were decreased obviously in 100HI group at the age of 60 day.Iodine excess can cause brain under development in their filial generation,and the pathogenesis maybe related to hypothyroidism induced by iodine excess.