The aim of this work is a comparative study of the absorption of glucose and fructose in the small intestine of white rats with high and medium levels of constitutional stress reactivity. The rats were divided into two groups depending on the level of constitutional stress reactivity: 1 - high stress reactivity; 2 – the average level of stress reactivity. Constitutional stress reactivity was assessed using a set of behavioral tests and analysis of histopathological differences in the tissues of the stomach, thymus, and adrenal glands in some of the animals of each group after immobilization stress. To study the absorption of monosaccharides, the method of perfusion of an isolated loop of the small intestine in vivo was used. It was found that in rats with an average level of stress reactivity, the rate of glucose absorption at its initial concentrations in the cavity of an isolated loop of the small intestine of 25 and 50 mM was higher by 24–26% (P < 0.05) compared to animals with high stress reactivity. The absorption rate of fructose (25 and 50 mM) is higher in rats with an average level of stress reactivity compared to animals with high stress reactivity by 32-38% (P < 0.05). It was found that the main role in the adaptive rearrangement of glucose absorption to the level of constitutional stress reactivity is played by the transport system mediated by the SGLT1 transporter. A study of the kinetics of glucose absorption in the small intestine under the influence of an inhibitor of its active transport mediated by the SGLT1 transporter, phloridzin (2 mM), showed that in animals with an average level of constitutional stress reactivity, compared with animals with a high level of it, there is a significant increase in such an important constant of active glucose absorption as the maximum transport rate (Jmax), a significant decrease in the rate constant of unsaturable absorption (Kd), while the Michaelis constant (Kt) does not change significantly. Therefore, in animals with an average level of constitutional stress reactivity, a higher coefficient of efficiency of the active glucose transport system through the apical membrane of the intestinal cell (Jmax/Kt) is observed compared to animals with a high level of stress reactivity (more than 1.5 times). Thus, the results obtained demonstrate the existence of a relationship between the genetically determined stress reactivity of the body and the transport function of the small intestine.