Objective:To explore the apoptosis rate of thyroid cells from normal,Graves disease(GD),Hashimoto thyroiditis(HT) and detect the apoptosis related proteins. Methods:The apoptosis rate of thyroid cell from normal GD and HT thyroid gland was measured by the terminal deoxynucleotidyl transferase mediated d-UTP nick labeling(TUNEL),and apoptosis related proteins Fas and FasL were confirmed by immunohistochemical methods,and the expression of Fas mRNA was measured by RT-PCR. Results:Higher apoptosis rate was found in GD and HT TEC,and there was an obvious and almost equal expression of FasL(P > 0.05). The difference in expression of Fas protein and mRNA in three groups thyroid glands was significant (P < 0.01),and the expression of Fas in normal tissue was the lowest and trivial,but the Fas expression in HT was the highest and distinctive. Conclusion:These data indicate that apoptosis plays an important role in the pathogenesis of AITD,and Fas/FasL may be the signal molecule related to apoptosis of TEC.