Abstract: Objective: To investigate the influence of fluorine on the thyroid gland in mice.Methods: Eighty mice were randomly divided into control group and three experiment groups.The mice in control group,experiment groups with lower dose of fluorine and higher dose of fluorine group were injected physiological saline,NaF solution at 20 mg/L and 200 mg/L via peritoneal cavities,respectively.The mice in group with higher dose of fluorine mixed with selenium were injected solution containing NaF at 200 mg/L and Na₂SeO₃ at 100 mg/L via peritoneal cavities.After ten days(short-term) and thirty days(long-term),the serum levels of T₃ and T₄ in the mice were measured.Results: The serum levels of T₃ and T₄ had no obvious difference between the group with a low dose of fluorine and control group(P>0.05).The levels of T₃ and T₄ increased significantly in the group with high dose of fluorine and the level of T₄ was much higher than that in the control group(P<0.05).The levels of T₃ and T₄ had no significant differece between the group with higher dose of fluorine mixed with selenium and the control group,and the level was decreased compared with that of higher dose of fluorine group.Under long-term influence,the levels of T₃ and T₄ had no obvious difference between lower dose group and control group(P>0.05).Compared with control group,the level of T₄ of higher dose group was higher(P<0.05),while the level of T₃ was lower,but the difference was not obvious(P>0.05).The levels of T₃ and T₄ had no obvious difference between the group with higher dose of fluorine mixed with selenium and control group(P>0.05)Conclusions: Fluorine at a high dose might interfere the secretive function of thyroid gland in mice.It enhances the secretion of thyroid gland in short-term,but inhibits the secretive function in long-term.The changes of the secretive function of thyroid gland are correlative with the dose of fluorin and the time length of test.By supplying selenium,the secretive function of thyroid gland trends to come back to normal state from the disorder aroused by high dose of fluorin.