The relative expression of p27 using IHC was highest in the control group and lowest in the high-dose formononetin treatment group.<h4>Conclusions</h4>Formononetin treatment was shown to inhibit the proliferation of eutopic and ectopic endometria in patients with endometriosis through the regulation of p27, pSTAT3, and PR-B. The gene discussed is RB1; the disease is endometriosis.