【Objective】 There is evidence that thyroid hormones(TH) could affect on collagen development.Also there is some data that methylation play a significant role in fibrogenesis.That’s why the aim of the article was to find out if such pathomorphological changes in liver as fibrosis that were caused by TH could be associated with the changes of DNA methyltransferase activity.【Methods】 Experimental study was presented on 89 mature white rats.3 experimental groups were performed: 1-experimental hyperthyroidism,2-experimental hypothyroidism,3-control group.The thyroid profile for T3,T4,TTH and profile activity for DNA methyltransferase(DNMT) were determined.The weight of liver was examined.Microscopy and morphometry were performed.【Results】 In experimental hyperthyroidism and hypothyroidism the respective changes in TH concentrations occur with a normal level of TTH.It was revealed gender differences in TH levels under impaired thyroid status.In hypothyroidism a decrease of TH concentration occurs in females and males,but it is more expressed in males.In hyperthyroidism the increased concentrations of TH is observed in all rodents,but it is more significant in males.The weight of liver gain in hyperthyroid rodents and decreased of liver weight in hypothyroid rats.In experimentally hyperthyroidism the pathomorphological changed in liver were characterized as an acute vascular insufficiency,hypertension,inflammation,toxic effects of hormones,an initial stage of hepatitis with a high activity,traces of old hemorrhage and a marked fibrosis in the liver.Hypothyroidism also effects on the liver with the signs of acute vascular insufficiency,hypoxia,toxic effects of hormones,necrosis and mild fibrotic changes in the liver tissue.The enzymatic activity of DNMT was increased both in hyperthyroidism and in hypothyroidism.【Conclusions】 From results that were’ve obtained we could conclude that persistent shifts of TH cause pathomorphological changes in the liver.They were more expressed in hyperthyroidism.The significant correlation between the DNMT activity and fibrosis in hyperthyroidism was found out. Objective] There is evidence that thyroid hormones (TH) could affect on collagen development. Also there is some data that methylation play a significant role in fibrogenesis. Why is the aim of the article was to find out if such pathomorphological changes in liver as fibrosis that were caused by TH could be associated with the changes of DNA methyltransferase activity. 【Methods】 Experimental study was presented on 89 mature white rats.3 experimental groups were performed: 1-experimental hyperthyroidism, 2-experimental hypothyroidism, 3-control group The thyroid profile for T3, T4, TTH and profile activity for DNA methyltransferase (DNMT) were determined. The weight of liver was examined. Microscopy and morphometry were performed. [Results] In experimental hyperthyroidism and hypothyroidism the the quite changes in TH concentrations occur with a normal level of TTH.It was revealed that gender differences in TH levels under impaired thyroid status. hypothyroidism a decrease of TH con centration occurs in females and males, but it is more expressed in males. hyperthyroidism the increased concentrations of TH is observed in all rodents, but it is more significant in males. weight of liver gain in hyperthyroid rodents and decreased of liver weight in hypothyroid rats. experimentally hyperthyroidism the pathomorphological changed in liver were characterized as an acute vascular insufficiency, hypertension, inflammation, toxic effects of hormones, an initial stage of hepatitis with a high activity, traces of old hemorrhage and a marked fibrosis in the liver. Hypothyroidism also effects on the liver with the signs of acute vascular insufficiency, hypoxia, toxic effects of hormones, necrosis and mild fibrotic changes in the liver tissue. Enzymatic activity of DNMT was increased both in hyperthyroidism and in hypothyroidism. 【Conclusions】 From results that were’ve obtained we could conclude that persistent shifts of TH cause pathomorphological changes in the liver. They w ere more expressed in hyperthyroidism. The significant correlation between the DNMT activity and fibrosis in hyperthyroidism was found out.