A new alkaloid, kopreasin A (1) was isolated from the leaves of Kopsia arborea (Apocynaceae) together with ten known indole alkaloids (2-11), and the structure was elucidated by NMR spectral analysis using 2D techniques. These indole alkaloids showed a moderate vasorelaxant activity on isolated rat aorta ring. © The Japan Institute of Heterocyclic Chemistry.