Several studies have shown that plant-derived polyphenols reduce cardiovascular accidents in high-risk patients and the inhibition of platelet function may be responsible for part of this benefit. Lindera obtusiloba is widely used in traditional herbal medicine for the treatment of cardiovascular and inflammatory diseases. Therefore, the antiplatelet and antithrombotic activities of Lindera obtusiloba Extracts (LOE) on in vitro platelet aggregation, radical scavenging activity and in vivo murine pulmonary thrombosis were examined. LOE was able to directly scavenge the stable DPPH radical in a concentration-dependent manner and its $IC_{50}$ value was 3.9 ${pm}$ 0.1 ${mu}g$/ml. LOE significantly inhibited collagen- and ADP-induced platelet aggregation in a concentration-dependent manner and its $IC_{50}$ value is 0.9 ${pm}$ 0.1 mg/ml and 0.4 ${pm}$ 0.1 mg/ml respectively. The inhibitory effect of LOE was comparable to aspirin ($IC_{50}$ values were 1.0 ${pm}$ 0.5 and 1.0 ${pm}$ 0.7 mg/ml, respectively). Furthermore, oral administration of LOE suppressed the death of mice with pulmonary thrombosis induced by intravenous injection of collagen plus epinephrine. Taken together, our results suggest LOE may be a promising candidate for antithrombotic agent, and the antithrombotic effect of LOE may be due to, at least in part, antiplatelet activity.