【Objective】To assess the impact of siRNA transfection on the tumor development under experimental pathology of thyroid gland.【Methods】Experiments were performed on rats weighing(180±20)g,which were divided into five groups:IA and IB-animals with simulated hypo and hyperthyroid states and transplanted Guérin’s carcinoma;ⅡA andⅡB-animals with simulated hypo and hyperthyroid states and transplanted Guérin’s carcinoma in combination with siRNA transfection;Ⅲ-control group with transplanted Guérin’s carcinoma in combination with siRNA transfection.Orthogonal dimensions of the tumor was measured.Histological and immunohistochemical researches of tumor samples were performed.【Results】It has been shown that the inhibitory effect of short interfering RNA realized in a greater extent in hypothyroid state,indicating an important role of thyroid hormones in the regulation of expression of genes that control the cell cycle.【Conclusion】siRNA transfection leads to inhibition of tumor growth in animals with both hypo and hyperthyroidism,but this process is more obvious in hypothyroidism status. 【Objective】 To assess the impact of siRNA transfection on the tumor development under experimental pathology of thyroid gland. 【Methods】 Experiments were performed on rats weighing (180 ± 20) g, which were divided into five groups: IA and IB-animals with simulated hypo and hyperthyroid states and transplanted Guérin’s carcinoma; Ⅱ A and Ⅱ B-animals with simulated hypo and hyperthyroid states and transplanted Guérin’s carcinoma in combination with siRNA transfection; Ⅲ-control group with transplanted Guérin’s carcinoma in combination with siRNA transfection. Orthogonal dimensions of the tumor was measured.Histological and immunohistochemical researches of tumor samples were performed. [Results] It has been shown that the inhibitory effect of short interfering RNA realized in a greater extent in hypothyroid state, indicating an important role of thyroid hormones in the regulation of expression of genes that control the cell cycle. 【Conclusion】 siRNA transfection leads to inhibition of tumor growth in animals with both hypo and hyperthyroidism, but this process is more obvious in hypothyroidism status.