OBJECTIVE: To explore the effects of Taohong Siwu decoction(桃红四物汤, THSWD) on the extracellular matrix of endometrium in rats following drug-induced abortion.METHODS: Thirty-six pregnant female rats were administered mifepristone and misoprostol to induce abortion, and amounts of uterine bleeding were recorded. Pathological damage and collagen accumulation were detected by hematoxylin-eosin staining and Masson's trichrome staining in uterus, respectively. Myeloperoxidase was evaluated by immunohistochemistry.The expression levels of fibronectin, laminin, matrix metalloproteinase 9(MMP-9), and tissue inhibitor of metalloproteinase 1(TIMP-1) were quantified using western blotting.RESULTS: THSWD could promote endometrial protection in rats following drug-induced abortion.The contents of cellulose and myeloperoxidase were significantly decreased in uterine tissue of THSWD-treated groups. Moreover, THSWD significantly decreased the expression levels of fibronectin, laminin, and TIMP-1. THSWD also significantly increased MMP-9 expression and the MMP-9/TIMP-1 ratio.CONCLUSION: THSWD plays a critical role in endometrial protection by reducing extracellular matrix deposition and uterine fibrosis. These effects may have been achieved by increasing MMP-9, reducing TIMP-1, and/or altering the ratio of MMP-9/TIMP-1.