The article presents results of histological, histochemical investigations of duodenal mucosa of broilers, which were fed 36 days in a row with were fed 36 days in a row with fodder mixed of probiotic supplements «Probion forte» in doses of 100 g/kg. At 36 day of the experiment 10 chickens from each group were taken out from the experiment, was performed autopsy and selected models of duodenum, which are fixed in 10% of solution neutral formalin, Karnua liquid, followed by pouring into paraffin. It was produced histological sections, were stained with hematoxylin-eosin, by Stidmen, McManus. Prolonged feeding of poultry with probiotic supplements «Probion forte» in excessive dose of 100 g/kg has caused structural and functional changes in the mucosa of the duodenum, expressed the formation of ugly bifurcated broad villi and reflected a decrease in productive indexes of poultry.