Abstract: OBJECTIVE To investigate the effect of Yinning tablet on gene expressions of thyroid hormone receptor (TR) and type I iodothyronine deiodinase (DioⅠ) and activity of DioⅠ in liver tissues of rat with hyperthyroidism liver damage. METHODS Rats were perfused intragastrically with Levothyroxine sodium tablets(800 mg·kg^-1·d^-1) to establish the rat model of hyperthyroidism-induced liver injury. Rats were treated with Yinning tablets at 0.6, 1.2, 2.4 g·kg^-1·d^-1 and Jiakangling at 1.2 g·kg^-1·d^-1 for 30 days, respectively. After treatment, liver samples were immediately collected. The levels of gene expressions of TRα1, TRα2, TRβ1 and DioⅠ in liver tissues were determined by real-time quantitative PCR, meanwhile, the DioⅠ level was detected with enzyme-linked immunosorbent assay, and the activity of DioⅠ was tested with Chopra’s method. RESULTS Compared with control group, the mRNA expressions of TRa1 and TRb1 were up-regulated and the expression of TRa2 was down-regulated(P<0.01), the content and activity of DioⅠ were increased(P<0.01 or P<0.05). Yinning tablet inhibited the the expressions of TRa1 and TRβ1 genes(P<0.05), but no statistical difference was noted on the expression of TRa2(P>0.05). Compared with the control group, the level of gene expression and activity of DioⅠ in model group was significantly increased(P<0.01, P<0.05). Compared with the model group, Yinning tablet significantly inhibited mRNA expression of DioⅠ in a dose-dependent(r=-0.792, P<0.01) way. Yinning tablet in different dosage groups could decrease the level of DioⅠ(P<0.05, P<0.01), Yinning tablet in medium and high groups could significantly reduce DioⅠ activity(P<0.05). CONCLUSION TR and DioⅠ expression in liver tissue might be involved in the occurrence of Hyperthyroidism liver damage. Yinning tablet may adjust the expressions of TR and DioⅠ genes and inhibit the content and activity of DioⅠ in liver tissues of rat with Hyperthyroidism liver damage, which may be one of the molecular action mechanisms through which Yinning tablet prevents Hyperthyroidism liver damage.