Triclabendazole is the drug of choice against Fasciola spp. infections in humans and animals. However, parasitic resistance against triclabendazole is spreading in the veterinary field. The objective of this study was to assess of flukicide efficacy of triclabendazole through evaluation of the histopathology of Fasciola hepatica adult fluke’s specimens. For this, the efficacy test was performed on naturally infected sheep treated with triclabendazole (Fazinex®) at the dose recommended for F. hepatica, in which the flukes recovered at necropsy on the 7th day post-treatment and separated for histological examination. The teguments and intestines from F. hepatica recovered from treated and control sheep were examined by microscopy. In the outer and inner parts of the tegument, edema and swelling of its structural components are noted. The spines in the tegument were enlarged, swollen, take on a more rounded shape and have changes in color, perceiving the eosinophilic dye in greater concentration. There was a detachment of the brush border of the intestinal epithelium and the accumulation of microvilli of the apical part of the epithelium in the intestinal lumen. The cellular structures of the intestinal epithelium were melted. The results indicated that the teguments and intestines of F. hepatica were severely affected by triclabendazole and demonstrated the importance of the use of histopathology for the diagnosis of therapeutic efficacy in field strains.