West Siang is an administrative district in the state of Arunachal Pradesh in India.

In 1989 territory was given from West Siang to the East Siang district. Since 1999, this territory has been in the new Upper Siang district. Archaeological finds from Malinithan site in West Siang are on displayed at the Jawaharlal Nehru Museum, Itanagar.[citation needed] west siang is now been divided into upper siang and lower siang.

The district headquarters are located at Aalo. West Siang district occupies an area of 8,325 square kilometres (3,214 sq mi), comparatively equivalent to Crete.

The 2,000-kilometre-long (1,200 mi) proposed Mago-Thingbu to Vijaynagar Arunachal Pradesh Frontier Highway along the McMahon Line, (will intersect with the proposed East-West Industrial Corridor Highway) and will pass through this district, alignment map of which can be seen here.

There are seven Arunachal Pradesh Legislative Assembly constituencies in this district: Liromoba, Likabali, Basar, Along West, Along East, Rumgong, and Mechuka. The first six are part of Arunachal West Lok Sabha constituency, while Mechuka is part of Arunachal East Lok Sabha constituency.

According to the 2011 census West Siang district has a population of 112,272, roughly equal to the nation of Grenada. This gives it a ranking of 612th in India (out of a total of 640). The district has a population density of 13 inhabitants per square kilometre (34/sq mi). Its population growth rate over the decade 2001–2011 was 8.04%. West Siang has a sex ratio of 916 females for every 1000 males, and a literacy rate of 67.62%.

Various tribal groups of the Adi people, Memba and Khamba tribes live in the district. The Adi follow generally follow Donyi-Polo, although some have embraced Baptist Christianity in recent years. The Memba and Khamba are followers of Tibetan Buddhism. A well-known Tibetan Buddhist temple, Mechuka Gompa, is located in the western part of the Memba-speaking Mechuka district of West Siang.

Languages spoken include Adi, a Sino-Tibetan tongue with approximately 140 000 speakers, written in both the Tibetan and Latin scripts; and Galo, an endangered language with 30 000 speakers, also in the Sino-Tibetan language family.

The district is rich in wildlife. Rare mammals such as Mishmi takin, Snow leopard, Red panda and Musk deer occurs while among birds there is the rare Blyth’s Tragopan. A flying squirrel, new to science has been recently discovered from this district. It has been named as Mechuka Giant Flying Squirrel Petaurista mechukaensis.

In 1991 West Siang district became home to the Kane Wildlife Sanctuary, which has an area of 55 km2 (21.2 sq mi).