Background: The goal was to investigate the inhibitory effect of formononetin, an active component in Astragalus membranaceus, on the pathogenesis and development of esophageal cancer and the mechanism of action.Methods: The expression of COX-2 in cancer tissue and paracancerous tissue of patients with esophageal cancer detected early. C57BL/6 mice were used to construct a 4-nitroquinoline 1-oxide (4-NQO)-induced esophageal can-cer model to verify the inhibitory effect of formononetin on the pathogenesis of esophageal cancer. Additionally, human esophageal cancer cells were treated with formononetin, and the effects on the proliferation and cell cycle of esophageal cancer cells were assessed by the CCK-8 assay and flow cytometry. Changes in the expression levels of cyclin D1 and COX-2 mRNA in cells were detected by RT-qPCR and western blot (WB) analysis.Results: The expression level of COX-2 mRNA in esophageal cancer tissue was significantly higher than that in paracancerous tissue. In the mouse cancer model, the incidence of esophageal cancer in mice in the formononetin treatment group was significantly reduced at week 18 (0/15 vs. 2/15) and at week 24 (6/15 vs. 13/15) (all p < 0.05). Formononetin significantly inhibited the proliferation ability of KYSE170 and KYSE150 cells and inhibited the protein expression of COX-2 and cyclin D1 (both p < 0.05).Conclusions: Formononetin, an active component of Astragalus membranaceus, can prevent the pathogenesis and progression of esophageal cancer by reducing the expression of the inflammatory proteins COX-2 and cyclin D1. (Clin. Lab. 2023;69:458-468. DOI: 10.7754/Clin.Lab.2022.220403)