Sepidium magnum is a species of beetles of the family Tenebrionidae.

Sepidium magnum can reach a body length of about 29–35 millimetres (1.1–1.4 in) and a body width of about 12–15 millimetres (0.47–0.59 in).

Body is brownish-black, while the head, prothorax, legs, and antennae show a pale fawn-coloured pubescence.

Prothorax has a large prominent rounded tubercle.

The surface of elytra is divided by two longitudinal sinuous carinse, with reticulating ridges on the sides.