Although cardiac amyloidosis is often associated with mitral valve disease due to amyloid deposits, severe mitral valve regurgitation in a patient with systemic amyloidosis is uncommon. We report a 38-year-old man with severe mitral valve regurgitation due to ruptured chordae. He underwent mitral valve repair and both leaflets of mitral valve appeared normal except for ruptured chordae. Postoperative histological results revealed the presence of the amyloid deposit in the mitral valve and ruptured chordae. The amyloid deposit might be a cause of ruptured chordae, which is a rare reason for mitral valve regurgitation in a patient with cardiac amyloidosis.