Little is known about the habits of this species, but it is supposed that like the other gibbons they are mainly frugivores, live in pairs and vocally mark their territory.
This species is endemic to the Chinese island of Hainan.
Until the 1960s widely distributed on the island, it is currently confined to the Bawangling nature reserve, on the western part of the island, where no more than twenty specimens have been registered. Like all gibbons of the genus Nomascus, the Hainan gibbon shows a clear sexual dimorphism in color.
Males are black while females are gray with a dark spot on the crown of the head and on the chest. The weight is between 7 and 8 kg. Due to the small population and the narrowness of the range, the IUCN Red List classifies this species as critically endangered.
The Hainan gibbon is considered an umbrella species for the Hainan Island. This designation indicates that status of the Hainan gibbon is a marker for the health and stability of its ecosystem. Alterations in the characteristics of the Hainan ecosystem that negatively affect the gibbons are indicative of negative impact on other species as well.
The most recent count found 22 Hainan gibbons split between two families, one of 11 and one of seven members, with four loners, all residing in Bawangling National Nature Reserve on Hainan Island. Habitat loss is the primary cause in the decline of the Hainan gibbon.
Poaching has also been a problem. The secondary forests are less suitable for the Hainan gibbons than the primary forests. Their trees are shorter in height, and they severely lack resources, such as food and shelter, needed by the gibbons to survive.
The dwarf forest is even less favorable for the gibbons and a study by Fan et al. found that gibbons spent only 0.5% of the 13-month study period in dwarf forests. The Hainan gibbons have acquired some reproductive adaptations in response to their drastically decreased natural habitat.
The few remaining gibbons exhibit polygynous relationships; small families typically consist of one breeding male, two mature females, and their offspring. This stable pair bond relationship seems to have allowed the gibbons to decrease their interbirth interval, the length of time between births.