BACKGROUNDS: The use of tanniferous plants in ruminants has been documented as an alternative to anthelmintics, for the control of gastrointestinal nematodes. OBJECTIVES: The objective of this study was to assess the possible impact of Crataegus pseudomelanocarpa extract on the Trichostrongylids helminthes found in sheep. METHODS: Two groups of sheep were experimentally infected with 2.000 L3 of Trichostrongylids. After 4 weeks, Hawthorn Extract was diluted in 200 ml of water at 25 0C and was orally administered two times a day. The 8 remaining animals comprised as infected control group which received an equal volume of water daily during the same period of time. On the 9th day, all of the sheep were necropsied and calculations were made for individual egg excretion adult worm counts in the abomasum and small intestines sex rate (male/female); and the fecundity rate. The results were compared using statistical test. Moreover, histological samples from the fundus and pyloric regions were taken to enumerate the number of mucosal mast cells, globule leukocytes and eosinophils. RESULTS: The results showed that the administration of this tanniferous plant was associated with a significant decrease in egg excretion (82.57%) and female fecundity (84.85%). Pathological findings showed a greater presence of mucosal eosinophils and mast cells in the abomasums and small intestines of the control group in compare with treated sheep. However, statistical analyses did not show a significant difference between these groups. CONCLUSIONS: These results indicate that the administration of Crataegus pseudomelanocarpa, which has tannin extract, could be effective in the control of Trichostrongylids infected sheep.