The aim of the study was to determine the role of Lp(a) level on left atrial thrombus formation and plasminogen activity in patients with chronic atrial fibrillation. Materials and Methods: Clinical, laboratory and transoesophageal echocardiographic data were collected from fifty consecutive non anticoagulated patients with chronic atrial fibrillation. They were divided into two groups according to Lp(a) level: Thirty patients were with Lp(a) level> 30mgldl (group I) and twenty patients had Lp(a) level < 30mgldl (group II). Results: There was no significant difference in left atrial size between the two groups (5.53 vs 5.08cm) (P > 0.05). group I showed a significant decrease of left atrial appendage (LAA) flow velocity (15.93vs 27.42cm/s) (p< 0.01) and a significant increase of spontaneous echo contrast (SEC) (2.0 vs 0.3%) (p < 0.01) A significant increase in fibrinogen level (480.7 vs 387.55mg/dl) (p< 0.01) and total cholesterol (193.17vs 143.3mgldl) (P< 0.01) were observed in group I. There was no significant difference in plasminogen activity and D-dimers level between the two groups I & II (p > 0.05). multiple regression analysis showed a positive correlation between Lp (a) > 30 mg/dl and high fibrinogen level. A negative correlation was observed between Lp(a» 30mg/dl and both left atrial appendage flow velocity and plasminogen activity. Conclusion: Elevated Lp(a) in chronic AF patients can be considered as a predictor for left atrial thrombus formation and thromboembolic risk. Long term anticoagulation should be considered in those patients. Key words: AF, Lp (a), plasminogen