Abstract: Objective To investigate the effect of different concentrations of fluoride and iodine in drinking water on children's dental fluorosis and thyroid function.Methods According to different concentration of fluoride and iodine in drinking water,four villages in two counties of Henan provine were classified as high fluoride and iodine,high fluoride,high iodine,and control area.Children who were born and grew in the four araeas were chosen for dental fluorosis examination with Deans method.The prevalence rate of the goiter,and the concentrations of FT₃,FT₄ and TSH in serum were detected with radio-mimunoassay method among the children.Results The prevalence of goiter in children from high fluoride and iodine,high fluoride,high iodine and control areas were 19.2%,12.7%,19.4%,and 8.3%,respectively.There was no significant difference in goiter prevalence among the four groups(P>0.05).The prevalences of dental fluorosis were 49.4% and 46.5% in the children lived in high fluoride and iodine area and high fluoride area,rsepectively.No dental fluorlsis case was found in high iodine and control area.There was no significant difference in the concentration of serum FT₃ among the children from the four areas(P<0.05).The content ratios of serum FT₄ and TSH in children from high fluoride and iodine area were higher than that of in the children from the other three areas(P<0.05).There were no significant diffeience in serum FT₄ between the children from high fluoride area,high iodine area and control area(P>0.05).The concentration of serum TSH of children from high fluoride and iodine area and high iodine area was higher than that of children from high fluoride area and control area.Conclusion High fluoride and iodine increase the prevalence of goiter.High iodine increases thd concentration of FT₄.Fluoride can increase the concentration of FT₄ under high iodine condition.