Abstract: To study the effect of high iodine on brain and intelligence development.Method The mice were divided into two groups. One group drank deionic water with 50μg/L,the other drank deionic water with 3000μg/L.After the third month,the mice mated and the young mice were obser ved.Results The absolute and relative weight of brain and hippocampus were lighter in high iodine group,but no statistical difference.The stereological analysis demontrated that the mean volume and surface of cortex pyramidal cells in high iodine g roup were smaller than that in middle iodine group(P<0.05).But the number density of cortex py ramidal cells in high iodine group was higher(P<0.05).It suggested that the development of poyramidal cells in high iodine group was retarded.Conclusion High iodine may have injury on the brain of young mice.