Osmia (Osmia) opima are black bees; females have long yellow-gray hairs on the face with intermixed black hairs on the frons and vertex (Romankova 1985). T1–T5 have white hairs on the discs, and T6 have brown hairs (Romankova 1985). Males have long thick hair; T1–T3 has reddish hair, T4 has reddish mixed with dark hairs, and T5 has reddish mixed with lighter hairs (Romankova 1985). Female body length is 12.5–16.3 mm, and male body length is 12–13 mm (Romankova 1985).
Osmia opima are very similar looking to O. longicornis, especially the females, which previous authors have been unable to differentiate (Romankova 1985). Males can be differentiated by dissecting them to view the gonostylus, which is not expanded apically in O. opima as it is in O. longicornis (Romankova 1985). S8 also varies and has recurved lateral projections about mid-way through in O. opima and is more rounded apically (Romankova 1985).
Osmia opima make nests in old wood; cells are composed of clay (Romankova 1985).
Osmia opima specimens have been recorded in southeastern Russia, northeastern China, and South Korea (Romankova 1985).