Two isoquinolones, anhydroberberillic acid (1) and methyl anhydroberberillate (2) were isolated first time from the roots of Phellodendron amurense var. wilsonii as well as two related known compounds, berberine (3) and 8-oxyberberine (4). Their structures were elucidated by extensive 1D, 2D NMR and MS spectral analysis. Occurrence of the isoquinolones and protoberberines in the same plant indicated the definite possibility of these metabolites biogenetically originated from berberine alkaloids. © 2006 The Japan Institute of Heterocyclic Chemistry.