The new N-benzyltetrahydroisoquinoline alkaloid nummularine has been isolated from the leaves of Berberis nummularia. On the basis of a study of its spectral characteristics (PMR, IR, and mass spectra), the structure of nummularine has been established as 6-hydroxy-N-(3′-hydroxy-4′-methoxybenzyl)-7-methoxy-1- methyltetrahydroisoquinoline.