A free floating ball thrombus in left atrium is very rare, only 2 cases that develop ball thrombus after mitral valve replacement (MVR) have been reported. This case was a 55-year-old female who underwent MVR and tricuspid annuloplasty (TAP) in 1978. After 16 years, she developed replaced mitral valve stenosis due to pannus formation and tricuspid regurgitation (TR), with a free floating ball thrombus in the giant left atrium. A ball thrombus was taken out, and Re-MVR and tricuspid valve replacement (TVR) was carried out. Post operative course was uneventful. Because a free floating ball thrombus easily causes "Hole-in-one" sudden death, early surgical treatment must be considered.