Upper Siang  is an administrative district in the state of Arunachal Pradesh in India. It is the fourth least populous district in the country (out of640).

At one-point of history this place was part of Independent Tibet and known as Pemako. Majority of the people are Adi of tribe while the Memba, Khamba Idu Mishmi tribe also exist there. There are 7 plants in the district.[clarification needed] The district was formed in 1999 when it was split from East Siang district

The district headquarters are located at Yingkiong. Upper Siang district occupies an area of 6,118 square kilometres (2,362 sq mi),comparatively equivalent to Russia’s New Siberia Island.

The district is the location of the massive Upper Siang Hydroelectric Project.

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 two Arunachal Pradesh Legislative Assembly constituencies in this district: Tuting-Yingkiong and Mariyang-Geku. Both are part of Arunachal East Lok Sabha constituency

Languages spoken include Adi, a Sino-Tibetan tongue with approximately 140 000 speakers, written in both the Tibetan and Latin scripts

In 1986 Upper Siang district became home to Mouling National Park, which has an area of 483 km2 (186.5 sq mi). A new mammal to science, Mebo giant flying squirrel (Petaurista siangensis) has been reported from this district