Berberis thunbergii (Japanese barberry or Thunberg's Barberry, also Red Barberry) is a species of Berberis, native to Japan and eastern Asia.
It is a dense, deciduous, spiny shrub which grows 1-2 (3) m high. It has deeply grooved, brown, spiny branches with a single (occasionally tridentine) spine (actually a highly modified leaf) at each shoot node. The leaves are green to blue-green, very small, spatula to oval shaped, 12-24 mm long and 3-15 mm broad; they are produced in clusters of 2-6 on a dwarf shoot in the axil of each spine. The flowers are pale yellow, 5-8 mm diameter, produced in drooping 1-1.5 cm long umbrella-shaped clusters of 2–5; flowering is from mid spring to early summer. The edible fruit is a glossy bright red to orange-red, ovoid berry 7-10 mm long and 4-7 mm broad, containing a single seed. They mature during late summer and fall and persist through the winter.