Objective To investigate the change and clinical significance of thyroid CT value in patients with Graves disease and Hashimoto' s thyroiditis (HT).Methods One hundred and twelve Graves patients (GD group),54 HT patients (HT group) and 36 healthy people (NC group) were selected as our subjects.Computed tomography (CT) value of thyroid were measured.Results The CT value of the left thyroid gland was (70.53 ± 15.44) Hu in GD group,while (70.50 ± 16.01) Hu at the right side.In HT group,the CT value of the left thyroid gland was (53.77 ± 4.88) Hu,and (52.38 ± 6.67) Hu at the right side.The CT value of the left and right sides was (99.66 ±9.80) Hu and (100.77 ± 10.66) Hu in the NC group respectively.The CT value of GD and HT group were lower than that of the NC group (P ＜ 0.01),and the CT value of the HT group lower than that of the GD group more significant (P ＜ 0.01).Conclusion (1) The CT value of the GD group and the HT group are significantly lower than the NC group and the CT value of the HT group reduces more apparently than that of the GD group.(2) CT values can be used as an early,non-invasive diagnosis of GD and HT secondary indexes.