Abstract2‐(1‐hydroxypentyl)‐benzoate (dl‐PHPB), a derivate of 3‐n‐butylphthalide (NBP), is a novel therapeutic agent for treatment of cerebral ischemia. In the present study, the antiplatelet and antithrombotic activities of dl‐PHPB were evaluated in ex vivo platelet aggregation and in vivo arteriovenous (A‐V) shunt models. dl‐PHPB inhibited platelet aggregation induced by adenosine diphosphate (ADP), arachidonic acid (AA), and collagen (COL) in a dose‐dependent manner when given orally (12.9–129.5 mg/kg). The inhibitory potency was similar to 3‐n‐butylphthalide (NBP) and aspirin (ASP). Inhibition on platelet aggregation was also observed after iv administration of dl‐PHPB (1.29–12.9 mg/kg). The time‐course of these effects showed the maximal inhibition on platelet aggregation at 1 h after oral administration and 30 min after iv injection. dl‐PHPB (12.9–129.5 mg/kg, p.o.) caused dose‐dependent inhibition of thrombus formation in the rat A‐V shunt thrombosis model. These results show that dl‐PHPB is an orally and iv antiplatelet and antithrombotic agent and may be useful for treatment of ischemia stroke. Drug Dev Res 63:174–180, (2004). © 2004 Wiley‐Liss, Inc.