It is the largest species of slow loris, measuring 26 to 38 cm (10 to 15 in) from head to tail and weighing between 1 and 2.1 kg (2.2 and 4.6 lb).

Like other slow lorises, it has a wet nose (rhinarium), a round head, flat face, large eyes, small ears, a vestigial tail, and dense, woolly fur.

Its diet primarily consists of fruit, but also includes insects, tree gum, snails, and small vertebrates.

The species lives in small family groups, marks its territory with urine, and sleeps during the day by curling up in dense vegetation or in tree holes.

In traditional medicine, it is primarily used by wealthy to middle-class, urban women following childbirth, but also to treat stomach problems, broken bones, and sexually transmitted diseases.

Formerly considered a subspecies of the Sunda slow loris (N. coucang), it was recognized as a distinct species in 2001 by taxonomist and primatologist Colin Groves.

Although most of the recognized lineages of Nycticebus (including N. pygmaeus, N. menagensis, and N. javanicus) were shown to be genetically distinct—the analysis suggested that DNA sequences from some individuals of N. coucang and N. bengalensis apparently share a closer evolutionary relationship with each other than with members of their own species.

The authors suggest that this result may be explained by introgressive hybridization, as the tested individuals of these two taxa originated from a region of sympatry in southern Thailand.

[7] This hypothesis was corroborated by a 2007 study that compared the variations in mitochondrial DNA sequences between N. bengalensis and N. coucang, and suggested that there has been gene flow between the two species.

[15] The Bengal slow loris has a small swelling on the ventral side of its elbow called the brachial gland, which secretes a pungent, clear oily toxin that the animal uses defensively by wiping it on its toothcomb.

[16] The oil has been analyzed using gas chromatography coupled to mass spectrometry, and it has been shown that almost half of the several dozen volatile or semi-volatile chemicals present do not occur in the closely related pygmy slow loris.

[17] The authors of the study suggest that the chemically complex oils may help the lorises communicate with each other, allowing them to transmit by scent information about sex, age, health and nutritional status, and dominance.

[18] The preferred habitats of the Bengal slow loris range across tropical and subtropical regions, and include evergreen and semi-evergreen rainforests with forest edges and continuous, dense canopies.

The Bengal slow loris feeds on plant exudates such as sap, gums, resins, and latexes, particularly those from the family Fabaceae.

Even though the species does not have keeled nails, it will scrape the plant, actively breaking its surface; this behavior resembles that of marmosets and the fork-marked lemurs.

The bastard myrobala (Terminalia belerica), a deciduous tree common in Southeast Asia, is a preferred source for exudates,[22] but it has also been observed taking plant exudates from a number of families: Moraceae (Artocarpus), Magnoliaceae (Manglietia), Fabaceae (Acacia, Bauhinia), Lecythidaceae (Careya arborea), and Sterculiaceae (Pterospermum).

[9] Although it will feed on large insects (such as katydids and crickets),[23] gum, snails, small birds, and reptiles, it is primarily frugivorous.

[20] A nocturnal animal, the Bengal slow loris has excellent night vision, enhanced by a tapetum lucidum—a layer of tissue in the eye that reflects visible light back through the retina.

[6] It is the only nocturnal primate found in the northeast Indian states,[24] which include Assam, Mizoram, Nagaland, Meghalaya, Manipur, and Tripura.

In Burma, it has been reported from Bhamo, Sumprabum, Kindat, Chin Hills, Pathein, Thaungdaung, and Pegu; populations in Laos have been recorded in the north, central, and southern portions of the country.

[8] Listed as "Data Deficient" as recently as 2006 on the IUCN Red List, the Bengal slow loris was evaluated in 2020 by the International Union for Conservation of Nature (IUCN) as endangered-a decision based solely on habitat loss due to lack of sufficient field data.

[26] The most severe threats facing the species are the wildlife trade (trapping for exotic pets and use in traditional medicine) and deforestation.

Populations have been declared locally extinct in southern Quảng Nam Province and parts of the highlands, and the same is expected in Song Thanh and Kon Cha Rang nature reserves.

The Bengal slow loris may be restricted to a few isolated populations and is in serious threat of becoming locally extinct in parts of Assam and Meghalaya.