The natural endotoxin lipopolysaccharide has a powerful effect on uterine function, reducing animal reproductive capacity. Our work aimed to study the impact of lipopolysaccharide on the contractile activity of the uterine myometrium under ex vivo conditions. All testing of isolated longitudinal strips of the uterine horns from sexually mature female Wistar rats, perfused at 37°C with oxygenated Krebs solution, was con- ducted in isometric mode. Lipopolysaccharide was added to the perfusion solution at concentrations of 0.1, 0.5, and 1.0 μg/ ml. It was shown that lipopolysaccharide increased the tension of isolated strips of uterine myometrium, as evidenced by a significant increase in the amplitude of spontaneous contrac - tions, the area under the curve of contractions, and the duration of contractions, with maximum increases of 13% and 30% (at a concentration of 1.0 μg/ml), and 23% (at a concentration of 0.5 μg/ml), respectively. The greatest effect on the contrac - tile function of the uterine myometrium was observed with lipopolysaccharide acting at concentrations of 0.5 and 1.0 μg/ml. At the same time, endotoxin significantly increased the duration of the contraction-pause cycle and reduced the frequency of spontaneous contractions. Significant changes in the maximum rate of contraction (up to 30%) and relaxation (up to 19%) of myometrium strips indicate an imbalance in the contractile function of the uterine myometrium. Thus, lipopolysaccharide-induced increase in contractile activity and uterine myometrium dysfunction may be the cause of the deterioration of the reproductive ability of females.