Aim: During normal placentation, the uterine spiral arteries are remodeled to form high-flow, low-resistance vessels, which is necessary to meet the increasing demands of the fetus for blood and oxygen. Remodeling of uterine arteries is mediated by extravillous trophoblasts, which penetrate the arterial walls and induce the endothelial apoptosis. But the mechanism of endothelial apoptosis is not yet fully understood. In this study, we investigate the involvement of matrix metalloproteinase 9 (MMP-9) in trophoblast-induced endothelial apoptosis. Methods: MMP-9 small interfering RNA (siRNA) was transfected into extravillous trophoblasts (TEV-1) by lipofectamine. After transfection, the levels of MMP-9 and Fas Ligand (FasL) mRNA were assessed using real-time polymerase chain reaction (PCR), and the intracellular or extracellular levels of these proteins were measured using enzyme-linked immunosorbent assay. Then, trophoblasts transfected with MMP-9 siRNA or control siRNA were co-cultured with endothelial cells, respectively, in a transwell system. The apoptosis of endothelial cells was detected with flow cytometry. Results: MMP-9 mRNA was significantly decreased in MMP-9 siRNA-treated cells as compared with the control. However, FasL mRNA appeared unaffected. After transfection with MMP-9 siRNA, the intracellular and extracellular MMP-9 proteins were both efficiently decreased, as the soluble FasL protein, while the intracellular FasL protein was increased. Trophoblasts transfected with MMP-9 siRNA led to significant inhibition of endothelial apoptosis as compared with the control. Conclusions: Our results suggest that MMP-9 secreted by trophoblasts contributes to endothelial apoptosis via extracellular release of soluble FasL.