It is clear that the chemical structure of a drug and its process, which are the determinants of the degree of activity an anthelmintic have on the organs and tissues of trematodes, as well as their hosts. This study demonstrates changes in the microstructure of the small intestine of sheep with impulsive Paramphistomiasis after treatment with Antitrem. Seven days after giving “Antitrem (contain oxyclosanide and pyrantela pamoate, OLKAR Release, Russia)" at a dose of 200 mg/kg once perorally, fixed in 70% alcohol and administered according to generally accepted histological methods, the small intestine of the sheep which it was administered to was impulsively attacked by Paramphistomum cervi. Partial atrophy of intestinal mucosa, common dystrophic changes in the epithelium, and destruction of individual goblet cells represented the microstructural changes in the small intestine of infected sheep with Paramphistomum cervi after treatment with Antitrem. Microstructural changes in the small intestine of the sheep are composed of proliferative procedures, a reduction in the content of carbohydrate compounds, and a change in the protein component in the tissues of the organ and stagnation of the secretory product in the cells.