The leaves of Oncoba spinosa grow alternately on the stem (spirally arranged).
The leaf is simple, bright green-coloured above and paler beneath. The leaf is chartaceous and glabrous on both sides.
The leaves have a 1 cm long petiole.
The leaf of Oncoba spinosa is 8-12 cm long and 4-6 cm wide. The shape of the blade is ovate, the apex is acute or acuminate, the base is rounded or cuneate and the margins are serrate.
The venation of the leaf is reticulate with a prominent midrib.