A new carbazole alkaloid, clausine-L together with 11 known compounds, safrole, glutinol, 132-hydroxy(132-R)-pheophytin-a, methyl pheophobide-a, scopoletin, steroidal glycoside [β-sitosteryl glucoside +stigmasteryl glucoside], 2-methoxy-4-(2-propenyl)phenyl-β-d-glucoside, 2,6-dimethoxy-4-(2-propenyl)phenyl-β-d-glucoside, p-hydroxybenzoic acid, rutin and nicotiflorin were isolated and characterized from the leaves of Clausena excavata. Their structures were elucidated by spectroscopic methods and/or chemical transformation. Among them, safrole showed significant antiplatelet aggregative activity which was induced by arachidonic acid and collagen. © 1993.