The stability of the intestinal immunity of the honey bee depends on the effects of various toxic substances. Especially when detecting some infectious diseases in apiaries, when using various antibiotics. The aim of the study was to study the effect of oxytetracycline on the morphological parameters of enterocytes of the midgut and the microbiological pool of the intestine. To do this, 10 days after the last treatment, for the next five days, 20 experimental bees were selected from each family, immobilized and the midgut dissected. The study of the folds of the midgut was performed on paraffin sections. The study was performed histopreparations, which were obtained at a distance of 5 mm from the beginning of the midgut. Sequentially arranged 10 folds were chosen for measurement. Morphometric parameters of enterocytes were obtained by measuring their height, width and area. It has been studied that three sprays of working solution of oxytetracycline at a dose of 900 mg, per family, with an interval of two days, adversely affects the morphological parameters of enterocytes of the midgut. On the segmental section, in the cranial direction, there is a decrease in the number of folds of the epithelium per unit area of the intestine. At the same time, the area of enterocytes is smaller by 14.9 % compared to the epithelial cells of control bees. For microbiological examination of the intestine was carried out sowing on nutrient media, followed by counting bacteria. It was investigated that the intestinal microorganisms of bees are represented by both gram-positive (Bacillus, Streptococcus, Staphylococcus) and gram-negative (Enterobacter, Escherichia, Mikrococus) bacteria, as well as fungi and yeasts. At the same time, enterobacteria (Enterobacter aerogenes and Escheriichia coli) and staphylococci (Staphylococcus varneri) are dominant in the microbiocenosis. In the intestines of bees, where the antibiotic got, no 100 % destruction of bacteria was detected, but changes were still observed. And they are associated with a decrease in their absolute number. The most negative effects were found for Bifidobacterium and Lactobacillus. In May, the maximum concentration of Lactobacillus plantarum was detected, which is normally 3.3 lg CFU/g. In September and October, some lactic acid bacteria are completely absent in the intestines of bees.