Marine brown algae of the family Dictyotaceae are rich sources of monocyclic, bicyclic, and tricyclic diterpenes. These molecules are responsible for a wide range of pharmacological and ecological functions, as antitumor and antiviral. Here, we analyzed the effect of the dolastane diterpene (4R, 9S, 14S)-4α-Acetoxy-9β,14α-dihydroxydolast-1(15),7-diene, isolated from the marine brown alga, Canistrocarpus cervicornis on blood clotting and platelet aggregation. The dolastane diterpene was able to inhibit either plasma or fibrinogen coagulation induced by thrombin as well as delayed coagulation in the recalcification test. The dolastane diterpene impaired, in a concentration-dependent manner platelet aggregation induced by collagen or adenosine diphosphate with no lysis on such cells. Thus, the dolastane diterpene maybe a promising source of natural inhibitors for hemostatic disturbs (clotting and platelet aggregation) leading to the discovery of drugs of potential use as antithrombotic and antiplatelet. In addition, the dolastane diterpene may be used as a molecular model for development of new antithrombotic agents giving new approaches to the management to the treatment of thrombotic disturbs.