Abstract： Objective To investigate the effects of different concentrations of sodium fluoride on the morphologic characteristics of primarily cultured thyroid cells of SD rats and in order to obtain important proof for approaehing the mechani8m of thyroid gland damage caused by fluoride.Methods Thyroid cells of SD rat were primarily culture for 96 hours,and cell density was adjusted to 5.0×108/L Cell suspension with 5 ml Wills seeded into 6 weII plates,after 12 hours,0(contr01),10.100,1000 μmol/L of sodium fluoride was added into the well, witll each well representing different level of treatment group.Finally the cultured thyroid cells were collected for morph010gic study.Results Under microscope,the transparency of the control thyroid cells Was good,and cells gathered in cluster and adhered to wall.But a lot of cells treated with fluoride suspended,and lost their transparency-under scaning delectron microscope,the control calls showed integrated membrane and tightness to each other,as well as clear boundary between cells normal proliferation.While the thyroid cells treated with 10,100 μmol/L sodium fluoride 0bviouslv shrinked and deformed,and the cells treated with 1000 μmol/L of sodium fluoride were broken-Conclusions nuoride can affect the growth and development of thyroid cell and damage the structure and morphology.Sodium fluoride affects the morphologie characteristics of thyroid cells in a dose-response manner.