The aim of the study was to determine the effect of repeated applications of aflatoxin B1 (AFB1) on immunocompetent cells (CD3 T cells) and alkaline phosphatase in the intestinal mucosa. Mice were orally treated with AFB1 for 24 days. The mucosa of the intestine showed a significant decrease in the number of CD3 T cells and a significantly lower level activity of alkaline phosphatase on day 24 in AFB1 treated mice. Similarly, with changes in the small intestine, qualitative haematological parameters were modified in systemic immunity as lymphopenia, and neutropenia, monocytopenia. AFB1 treated animals showed reduction in body weight gain and increased liver weight. We supposed that changes found in the small intestine are secondary to primary systemic haematological lesions. The decrease in CD3 T cells suggests a connection with the decrease in the host's resistance to infectious diseases.