Bates's sunbird is a very small dull green sunbird with a short, decurved bill a short tail and a yellowish belly. The male has dark olive upperparts, except for a vague pale supercilium, with paler greyer underparts with a pale buffy centre to the belly. The wings are dark brown with pale fringes and the tail is black with wide olive edges and tips to the outer tail feathers. There are long wispy yellow feathers on the sides of the breast, in the otherwise similar female these feathers are whiter and may be much reduced in length. They measure 9–10 cm in length and weigh 5.7–7g. Given the species overall drab plumage and furtive habits, it can be easily overlooked.
