Abstract: Objective: To study the relationship between serum free triiodothyronine (FT₃) and thyroid stimulating hormone (TSH) levels and the stability of carotid atherosclerotic plaques.Methods: 156 patients with carotid atherosclerotic plaques admitted to our hospital from October 2020 to October 2021 were selected as study subjects, and they were divided into unstable plaque group (89 cases) and stable plaque group (67 cases) according to the results of carotid ultrasound detection of plaque stability.Serum FT₃ and TSH levels were compared between the two groups.The factors influencing the stability of carotid atherosclerotic plaques were analyzed by logistic multi-factor regression analysis, and the predictive value of serum FT₃ and TSH levels for the stability of carotid atherosclerotic plaques were analyzed by receiver operating characteristic (ROC) curves.Results: The FT₃ levels in the unstable plaque group were lower than those in the stable plaque group, and the TSH levels were higher than those in the stable plaque group (all P< 0.05).The number of patients aged > 65 years, incidence of hypertension and LDL-C, TG and hs-CRP levels were higher in the unstable plaque group than in the stable plaque group (P< 0.05).Reduced FT₃ levels and increased TSH levels were independent risk factors for carotid atherosclerotic plaque instability (P< 0.05); the results of ROC analysis showed that the area under the ROC curve (AUC) of FT₃ combined with TSH to predict carotid plaque instability was 0.875, which was higher than that of single-factor predictions (P< 0.05), and the sensitivity and specificity of their combined diagnosis were 84.27%and 83.58%, respectively, which were not significantly different from that of single-factor diagnosis (P> 0.05).Conclusion: Both serum FT₃ and TSH levels are closely related to plaque stability in patients with carotid atherosclerotic plaques, and the combination of the two can improve the predictive efficacy for plaque stability.