This paper analyzes the effects of the infection caused by Toxoplasma gondii on the cat duodenal wall. Six cats (Felis catus) with 3-month-old were randomly divided into Control Group (G1; n = 3) and Infected Group (G2; n = 3). The animals from G2 received orarilly 200 T. gondii tissye cysts of ME49-strain (type II). After 40 days, the animals were submitted to euthanasia, laparotomy and had their duodenum removed, fixed in Bouin solution and submitted to histological routine obtaining 3 μm transverse cuts. The cuts were stained with Hematoxylin-Eosin (HE), Azan, Periodic acid-Schiff (PAS), Alcian-Blue, and Mallory trichrome. Qualitative assessment of the intestine wall as well as comparative measurements with respect to the thickness of mucosa, muscle tunic, total wall, the height of the villous, the depth of the crypts, and the height of the enterocytes and their nuclei were carried out. Calciform cells, the intraepithelial lymphocytes, and the Paneth cells were quantified. The results showed that the infection led to the atrophy of the mucosa, muscle tunic, and the intestinal wall of the duodenum of G2 cats (p < 0.05). The enterocytes height presented significant (p < 0.05) increase for G2 animals. According to the qualitative analysis, the collagen fibers were visibly taken a broader area on the intestinal wall layers, what suggests they have increased in size. Decrease in the sulphomucins secretion and the increase of Paneth cells were observed for these animals (p < 0.05).