The results of infecting the experimental pigs in Thai Nguyen Province with Trichocephalus suis (T. suis) indicate that the T. suis infected pigs have diarrhea, showing emaciation, pale mucous membrane, dry skin, bristly hair, growth retardation, multiple-ulcers in the cecum and colon, hyperemia and hemorrhage of the mucous, reduced rate of neutrophils, increased rate of eosinophils and major mono-nucleus compared with the control pigs. The infected pigs show the decrease of erythrocyte count, hemoglobin concentration and average volume of red blood cells, but they show the increase of white blood cell count and platelet count compared with the control pigs.