Sloth bears are distinguished from Asian black bears by their lankier builds, longer, shaggier coats, pale muzzles, and white claws. Adults are medium-sized bears weighing around 130 kg (290 lb) on average, though weight can range variously from 55 to 124 kg (121 to 273 lb) in females and from 80 to 192 kg (176 to 423 lb) in males. They are 60–90 cm (2.0–3.0 ft) high at the shoulder, and have a body length of 1.4–1.9 m (4.6–6.2 ft). Females are smaller than males, and have more fur between their shoulders.
Sloth bear muzzles are thick and long, with small jaws and bulbous snouts with wide nostrils. They have long lower lips which can be stretched over the outer edge of their noses, and lack upper incisors, thus allowing them to suck up large numbers of insects. The premolars and molars are smaller than in other bears, as they do not chew as much vegetation. In adults, the teeth are usually in poor condition, due to the amount of soil they suck up and chew when feeding on insects. The back of the palate is long and broad, as is typical in other ant-eating mammals. The paws are disproportionately large, and have highly developed, sickle-shaped, blunt claws which measure 10 cm (4 in) in length. Their toe pads are connected by a hairless web. They have the longest tail in the bear family, which can grow to 15–18 cm (6–7 in). Their back legs are not very strong, though they are knee-jointed, and allow them to assume almost any position. The ears are very large and floppy. The sloth bear is the only bear with long hair on its ears.
Sloth bear fur is completely black (rusty for some specimens), save for a whitish Y- or V-shaped mark on the chest. This feature is sometimes absent, particularly in Sri Lankan specimens. This feature, which is also present in Asian black bears and sun bears, is thought to serve as a threat display, as all three species are sympatric with tigers. The coat is long, shaggy, and unkempt, despite the relatively warm environment in which the species is found, and is particularly heavy behind the neck and between the shoulders, forming a mane which can be 30 cm (12 in) long. The belly and underlegs are almost bare.