Si-Donyi Festival is the major festival celebrated among the Tagin tribe of Arunachal Pradesh in North-eastern India. It is celebrated majorly in district headquarter Daporijo, in adjoining town Dumporijo and in Taliha, Siyum areas, also in state capital Itanagar, while in other places also it's being celebrated by Tagin community present there. The festival was first conceptualised in the year 1975 by Late Tatar Uli, who was the main pioneer in inception of Si-Donyi uyu. The other members who bore the responsibilities were Late Tadak Dulom and Popak Bage. The festival was celebrated in the same year under their guidance, and since then, the festival Si-donyi uyu has been celebrated by the Tagin tribe. The first priest who led the ritual was Dubi Nogam. Further the name Si-Donyi was suggested by Shri. Bingsa Kodak