Objective. To identify the molecular mechanisms of biological effect of ulipristal acetate (Esmya®) on uterine leiomyoma in vivo. Material and methods. A comparative immunohistochemical study of uterine leiomyomas removed from 16 women after 3 months of therapy with selective progesterone receptor modulator ulipristal acetate and 10 patients of similar age without hormone replacement therapy. Results. It was established that ulipristal causes the decrease of fibroids size due to the reduction of proliferative and mitotic activity combined with apoptosis induction. Conclusion. The observed trend towards increased expression of progesterone receptors by tumor cells is probably has a compensatory character. High level of Bcl-2 expression in combination with increased Bax expression and marked apoptosis induction suggests the effect of ulipristal on various ways of apoptosis regulation.