<p>The invention relates to a number of anticoagulant peptides and uses thereof. These peptides including the amino acid sequence of SEQ ID NO.1 and its derivatives, which are the inhibitor of coagulation factor XIa (fXIa). They significantly prolong the plasma activated partial thromboplastin time (aPTT) but no or little effect on the prothrombin time (PT). These anticoagulant peptides are useful anticoagulant agents for the treatment or prevention of thromboembolic disease with lowered bleeding risk.</p>
