This experiment has studied the changes in the liver in sheep during experimental infection with fascioliasis. Sheep were infested with 300 adoliskaria and observed changes up to 142 days. At the ultrastructural level in animals with fascioliasis, destructive changes were found in the liver. In the nucleus, the number of nucleoli decreases or they disappear completely, fragmentation of heterochromatin occurs and the content of euchromatin increases. The karyolemma exfoliates from the nucleus, as a result of which the perinuclear space expands. Mitochondria swell, they are polymorphic, and have an electron-dense matrix. At the beginning of the invasion, their number increases, and then their vacuolization, destruction occurs, while under the action of anthelmintic drugs and fasciolus toxins, the structure of the endolasmic network first of all changes: its cavities expand, then fragmentation occurs. Ribosomes are sprayed into the cytoplasm of the hepatocyte. It should be noted that under the influence of hexichol, acemidophene and thiopagol in the liver, membrane structures change most significantly and undergo necrobiosis.