Caesalpinia spinosa is a shrub or small tree up to 5 m high with reflexed prickles along its spreading spinose grey-barked densely leafy branches.
Leaves bipinnate, smooth or with sparse, short prickles; pinnae 2-3 pairs, often 10 mm long, with about 8 pairs of subsessile, firm, reticulate-veined, oblong-elliptic, glabrous leaflets, oblique at base, rounded at apex, about 2.5 cm long, 1 cm broad.
Flowers reddish-yellow, in narrow racemes 8-12 cm long; pedicels puberulent, 5 mm long, auriculate below the short calyx tube; larger calyx segments serrulate, about 6 mm long, the petals less than twice as long, about as long as the stamens.
Pods red, flat, 10 cm long, 2.5 cm broad, 4-7 seeded.
Seeds large, round and black at maturity.