Relevance. Fulvestrant is used for the treatment of breast cancer in combination with other drugs. The aim of the study was to determine the effect of the prenatal action of fulvestrant on the ovaries of the offspring of laboratory mice. Materials and Methods. The experimental animals were divided into 4 groups: intact, control and 2 experimental, 5 animals in each group. Injections were administered to females after fertilization at the gestational stage E 11.5 once intramuscularly. In the control group (n=5), sterile castor oil was administered at a dose of 0.8 mcg/kg. In the first experimental group (n=5), an antiestrogen was introduced in the form of an oil solution of fulvestrant 0.08 ml 0.0005% at a dose of 20 mcg/kg. In the second group (n=5), an antiestrogen was introduced in the form of an oil solution of fulvestrant 0.4 ml 0.0005% at a dose of 100 mcg/kg. Results and Discussion . The study revealed that in the ovaries when the drug was administered at a dose of 20 mcg/kg (F-20), the number of primordial follicles was reduced. Accordingly, the number of follicles of subsequent generations decreased. With the introduction of the drug fulvestrant 100 mcg/kg (F-100) on the section of the ovary, sclerosis of the stromal component is observed, accompanied by a rearrangement of the vascular network with signs of atresia and cystic degeneration of the follicular epithelium in the secondary and tertiary follicles, formed cysts are observed in the ovarian parenchyma. Conclusion. The prenatal effect of the drug fulvestrant on the maternal body during pregnancy leads to persistent structural changes in the ovaries of the offspring, manifested in the late stages of ontogenesis, which, in turn, can lead to violations of reproductive function. The depth and scale of these changes are dose-dependent.