A thrombus formation in the circulatory system due to failure of haemostasis causes vascular blockage and leads to serious consequences such as myocardial or cerebral infarction. Antiplatelet drugs are used to prevent formation of unwanted blood clot but their uses are associated with serious side effects. In association of efforts to develop natural products from plant origin as antiplatelet agent, Nigella sativa seeds were investigated for same. The platelet aggregation was monitored using spectrophotometer. The well known antiplatelet drug aspirin was taken as standard drug and activity was compared with it. Collagen was used as platelet aggregation inducer. 0.4 ml of 0.9mg/dl aspirin solution was used as standard dose. The final working concentration of aspirin and collagen was 18μg /ml and 2 μg /ml respectively. The aqueous extract was found to have antiplatelet activity. The 5.0μg/ml of seed extract was found 67% active against 18μg/ml of aspirin.