Abstract: To study the effect of Moniezia benedeni on local mucosal lymphoid tissues of small intestine in natural infected sheep, the intestinal tract of adult sheep (infected group) which natural infected by Moniezia benedeni were observed from macroscopic, microcosmic and submicrocosmic scales, and then compared with the normal ones (normal group). The results indicated that the average length of parasite in intestinal tract was 1.5 m, and the scolex mainly absorbed in the place where there was abundant Peyer’s patch of jejunum. Generally, the number of parasite was about 12. Opening the jejunum, it was easy to see that themucous membrane which lived by parasite increased thickness and was covered by many gray mucus, and there were also some punctuate hemorrhage on it. The results of microscope showed that the local mucosal epithelium was desquamate, and the number of epithelial cells, intraepithelial lymphocyte and goblet cells were all increased obviously under the integral mucosal epithelium; there were hyperemia in capillaries of lamina propria, and hyperplasia of lymphocyte, plasmocyte, diffuse lymphoid tissue and goblet cells of intestinal gland happened in different degree. There also had mortification in the part of intestinal gland in the place which located by scolex; under the mucous membrane, there was obvious hyperplasia in lymphatic nodules and Peyer’s patch, and part of this hyperplasia that protruded into lamina propria could form some new dome areas; There were a great quantity of eosinophilic granulocytes infiltrated among lamina propria, mucosal substratum and mucosal layers. Under scanning electron microscope, the mucosal epithelium of intestine was desquamate in infected group; The scolex which was covered with layer of compact microvillus of Moniezia benedeni was ellipsoid and had four sucking disk but without rostellum and canaliculus. The findings suggested that the thickening of intestinal mucous membrane was mainly caused by hyperplasia of autologous tissue against the uninterrupt stimulation from the microvillus at the surface of parasite. So it maybe the mechanism of to resist infection of Moniezia benedeni in adult sheep.