Cardiovascular diseases (CVDs) remain a leading cause of morbidity and mortality worldwide, with arterial thrombosis contributing substantially to acute cardiovascular and cerebrovascular events. Disruption of atherosclerotic plaques exposes thrombogenic components to circulating blood, triggering platelet adhesion, activation, and aggregation, which may ultimately result in arterial occlusion and ischemic complications. Platelet activation involves complex intracellular signaling pathways that promote granule secretion and amplify thrombus formation. Therefore, identifying compounds capable of suppressing excessive platelet activation remains an important strategy for preventing thrombotic disorders. Punicalin, a naturally occurring hydrolyzable ellagitannin, possesses diverse pharmacological activities, including hepatoprotective, neuroprotective, antiviral, antibacterial, and vascular endothelial protective effects. However, its effects on platelet function remain largely unexplored. Punicalin markedly inhibited human platelet aggregation induced by collagen and arachidonic acid, but had no significant effect on U46619. Furthermore, punicalin significantly reduced collagen-stimulated ATP release and P-selectin surface expression, indicating suppression of platelet granule secretion. Notably, punicalin attenuated phospholipase Cγ2 (PLCγ2) phosphorylation. Collectively, these findings demonstrate that punicalin effectively inhibits human platelet activation, particularly collagen-induced responses, in association with suppression of PLCγ2 phosphorylation and granule secretion. These results provide new insights into the pharmacological properties of punicalin on platelet activation.