Objective：To investigate the expression of transforming growth factor β1（TGF-β1）in serum and chordae tendineae tissue of patients with mitral valve chordae tendineae rupture，and to provide a basis for further understanding the promoting effect of TGF-β1 on mitral valve chordae tendineae lesion. Methods：20 patients with mitral chordae tendineae rupture admitted to the First Affiliated Hospital of Nanjing Medical University from May 2020 to December 2020 were selected as experimental group，and healthy examinees of the corresponding period were selected as normal group. Serum TGF-β1，clinical laboratory data and cardiac ultrasound data of all subjects were analyzed. Meanwhile，the ruptured mitral valve chordae in the experimental group and normal mitral tendinous chordae from 8 heart transplant recipients were collected during operation for immunohistochemical and electron microscope analysis. Results：The level of serum TGF-β1 in experimental group was significantly higher than that in control group（P < 0.05）. The left atrial diameter（LAD）and left ventricular end diastolic diameter（LVEDd） in the experimental group were significantly higher than those in the control group（P < 0.01）. Immunohistochemistry showed high expression of TGF-β1 and α-smooth muscle actin（α-SMA）in the ruptured chordae tendineae tissues. Scanning electron microscopy showed disordered arrangement of collagen fiber bundles in the ruptured chordae tendineae tissues. The loose layer（outer layer）was obviously thickened，stratified and broken end，and the dense layer（inner layer）had obvious cracks. Conclusion：TGF-β1 is highly expressed in the serum and ruptured chordae tendineae tissues of patients with mitral chordae tendineae rupture. It is suggested that it may be closely related to the occurrence and development of mitral chordae tendineae rupture.