Osmia quadricornuta are black bees with a blue or bronze-green metallic luster (Wu 2004). Females have erect golden-yellow hairs on the basal part of the clypeus, gena, vertex, and scutum. T1 is covered with long yellow-brown hairs, and T2–T5 are covered with long black-brown hairs (Wu 2004). In males, the paraocular area and clypeus are covered with dense white hair intermixed with a few black hairs, the vertex and the upper part of the gena have black to brown hairs, T1–T5 have yellow apical bands, and the discs of T2–T5 are covered in thin black hair (Wu 2004). Female body length is 11–12 mm, and male body length is 9 mm (Wu 2004).
Osmia quadricornuta specimens have been recorded in Yunnan province in China (Wu 2004).