The research was conducted to test feces of 1726 nomal buffaloes, 1760 normal cows and 357 diarrhea buffaloes, 387 diarrhea cows in 4 districts in Thai Nguyen provice. The results showed that: there were 67.23 percent of diarrhea buffalos and 67.96 percent of diarrhea cows infected Trichostrongylidosys in abomasum, in which 33.33 percent buffaloes and 43.35 percent cows were infectious with heavy and very heavy intensity. While the infectious intensity of normal buffaloes and normal cows were 46.12 percent and 49.77 percent respectively, and the most of them were infected with moderate intensity. The results of surgery examination on 197 buffaloes and 261 cows showed that: symtoms of buffaloes and cows infected Trichostrongylidosys in abomasum were anorexia, thin, dry skin, feathers ruffled and easy loss, pale mucous membranes, diarrhea for several days, loose, water barrels chest, abdomen. Trichostrongylidosys in abomasum caused damage, inflammation and hemorrhage in both the abomasum and small intestine, but it concentrated mainly in the abomasum with pathological changes such as lesions in mucous membranes, proliferation of cells in lower mucosal, damage of epithelial cells, lower mucosal with permeability oedema fluid (trauma, inflammation and hemorrhage will appear when the number of worms reach to 867-1732 individuals).