Abstract: ObjectiveIn order to further understand the role of iodine in the invasion of auto immune thyroid disease (AITD),effects exerted by different dietary iodine on the expression of Th1 type cytokine(INF-C)and Th2 type cy tokine (IL-10)in thyroid were investigated in experimental auto immune thyroiditis(EAT)rats.MethodsFemale Lewis rats were fed by low-iodine diet and drunk deionized water containing different concentration of KI respectively.Correspondingly,rats were divided into LI group,NI group and HIgroup.Induced EAT rats were passively immunized with Wistar rats.Tg.The thyroid tissue pathological changes were studied.Serum concentr at ion of anti-Tg autoantibodies were measured and the expression of INF-C and IL-10 genes in thyroid was analyzed.Results(1)EAT-induced rats from HIgroup had a more clearly lymphocytic infiltr ates indicating a more severe inflammation in thy roid glands while those from NI group appeared a mild infalmmation moreover in resto ration stage and rats from LI group just showed a light lymphocytic infiltrating within follicles.(2)The titer in EAT-induced rats was much higher than that of not induced EAT-rats,P<0.01.(3)The expression of INF-C and IL-10 in EAT-induced rats from HIwere both higher than its control group,P<0.05.The expresion of INF-C in EAT-induced,rats from NI and the expression of IL-10 in EAT-induced rats from LI were significantly increased compared with respective control group.ConclusionAmuch higherexpression of INF-C and IL-10 appeared in thyr oid glands of EAT rats from HI group which manifested an inflammatory reaction and anti-inflammation reaction.Only high expression of Th2 type cytokine IL-10 appeared in EAT rats from NI group with an inflammation in restoration stage and the expression of INF-Cin EAT rats from LI group revealed that the infamlmation was very lig ht and the process was slow.