Sun bears are the world’s smallest bears, standing 70 cm at the shoulder and 1.2 to 1.5 m from head to tail. Males are slightly larger than the females. They have short, wide, flat heads with small round ears. Their fur is rather coarse, but appears sleek. This coat is entirely black except for a "U" shaped patch on the chest and a gray to faintly orange muzzle. The yellowish or white chest patch is highly variable, "U" shaped in some and completely absent in others. This mark may exaggerate bears' sizes during fights. The young are born with soft, shiny coats. The paws are fairly large with sickle-shaped claws and naked soles which are thought to be helpful in climbing trees. These bears have an interesting walk, with all four legs turned in while walking.

Ranging from the eastern Himalayas to Sze-Chwan in China and throughout Burma and parts of Indo-China and Malaya, sun bears are found in dense lowland tropical forests where they are commonly found in trees.

Sun bears are active at night and are excellent and agile climbers. They sleep and sunbathe in trees. This species does not go through period of hibernation, probably due to the fact that they live in tropical areas and their food sources are present all year round.

This species is an opportunistic omnivore with bees, termites, and earthworms comprising the main part of its diet. Fruit is also eaten when available. The former are more regular food sources than fruit and usually there is no need for the bear to cover great distances in their search for food. These bears have long tongues that are helpful for obtaining insects from trees, termites from their nests, and honey from beehives. Should the opportunity present itself, sun bears will eat small rodents, birds, and lizards along with scavenging tiger kills. In human populated areas their diet may include rubbish, livestock and agricultural fruit such as bananas.

Little is known about the reproductive behavior of sun bears in the wild. Gestation period lasts about 95 days, but there is evidence of delayed implantation. Some sun bear pregnancies in a zoo in Fort Worth lasted 174 to 240 days. A sun bear at the Berlin Zoo actually gave birth two times in one year in 1961, first in April, then again in August, but this is rare. Litter size is usually around one to two but occasionally there are three. Newborns are blind, hairless, and helpless and weigh a mere 300 grams. Cubs stay with their mothers until fully grown and reach sexual maturity around three years of age.

Sun bears are one of the rarest bears. The exact number alive today is not known, but the population is steadily declining due to deforestation and hunting. Habitat destruction is causing these bears to live in smaller and more isolated patches. The land is being cleared to create coffee, rubber and oil palm plantations. Poachers are flocking to the protected areas and reserves because they know there are bears there. Reserves may not even be providing sufficient habitats for these bears because their needs are not completely known. Not many conservation attempts have been done to save these bears because so little is known about them. The gall bladders and other body parts of sun bears are used in folk medical practices. These bears are also quite commonly sold as pets.