Mahonia oiwakensis is a species of plant in the Berberidaceae family. It is native to China (Taiwan, Guizhou, Hong Kong, Sichuan, Taiwan, Xizang (Tibet) and Yunnan). It has been found at elevations up to 3800 m. Mahonia oiwakensis is a shrub or tree up to 7 m tall. Leaves are up to 45 cm long, compound with 12-20 pairs of leaflets plus a larger terminal one, dark green above, yellow-green below. Inflorescence is a fascicled raceme up to 25 cm long. Berries are egg-shaped, dark blue, sometimes almost black, up to 8 mm long.