A new dihydroberberine alkaloid, 7,8-dihydro-8-methoxyberberine (1), along with six known compounds including two dihydroberberine alkaloids, 7,8-dihydro-8-hydroxyberberine (2) and oxyberberine (3) and four protoberberine alkaloids, berberine (4), palmatine (5), jatrorrhizine (6) and columbamine (7), were isolated from the stems of Mahonia japonica. These compounds were characterized and identified by physical and spectral evidence.