Gibbon Wildlife Sanctuary or Hoollongapar Gibbon Sanctuary is an isolated protected area of evergreen forest located in North East India India. The Hoollongapar Gibbon Sanctuary contains India's only gibbons - the hoolock gibbons, and Northeastern India's only nocturnal primate - the Bengal slow loris. The upper canopy of the forest is dominated by the Hollong tree (Dipterocarpus macrocarpus), while the Nahar (Mesua ferrea) dominates the middle canopy. The lower canopy consists of evergreen shrubs and herbs. At the time, it was considered an "integral part" of the foothill forests of the Patkai mountain range. Although the sanctuary is currently completely surrounded by tea gardens and a few small villages, it used to connect to a large forest tract that ran to the state of Nagaland
Area: 20.98 sq. km.
Altitude: 100 to 125 msl 
Rainfall: 2‎‍,000 to 3,400 mm
Temperature: 6˚ to 35˚C
Vegetation: Tropical Semi-Evergreen Forest
Best time to visit: October to March

Key species:
Mammal: Gibbon Wildlife Sanctuary holds an important place for it's BIO-DIVERSITY , as it houses Seven out of only 15 species of Primate in India . The sanctuary has a rich biodiversity and is home to the only apes in India, the western hoolock gibbon (Hoolock hoolock), as well as the only nocturnal primate found in the northeast Indian states, the Bengal slow loris (Nycticebus bengalensis). Other primates include the stump-tailed macaque (Macaca arctoides), northern pig-tailed macaque (Macaca leonina), eastern Assamese macaque (Macaca assamensis assamensis), rhesus macaque (Macaca mulatta), and capped langur (Trachypithecus pileatus). Also found at the sanctuary are Indian elephants, tigers (Panthera tigris), leopards (Panthera pardus), jungle cats (Felis chaus), wild boar (Sus scrofa), three types of civet, four types of squirrel, and several other types of mammal.
 Birds : It is Recognized as Important Bird Area situated in Assam(IBA) by Bird Life International because it is habitation of almost 250 different species of birds of which several are extinct  including White Rumped Vulture, Long-Billed Vulture, Lesser Adjutant Stork, White winged Duck etc.