Nagsankar Mandir is situated 15 km  west of Biswanath chariali town, in a place called Sootea. The exact history of the temple is not definite. It was built around 4th Century AD. According to one belief, the temple was built by a King called Nag Sankar from Lohitya dynasty in the late 4th century. Nagsankar reigned eastern Kamrup (ancient name of Assam) in 378 AD. He was a great king and sent his representatives to his contemporary the Great Asoka of Maurya dynasty. 

According to another belief, the Nagsankar temple was built by king Nagmatta. Nagmatta is another name of the powerful king of Assam, Arimatta. Arimatta has an important place in mythology too. He is believed to be the son of the river-god Brahmaputra, who blessed the beautiful wife of king Ramchandra with a son. 

Ahom king Su-sen-pha repaired Nagsankar temple in 1480. With this work the king was able to spread his kingdom to the north bank of the river Brahmaputra and win the faith of the people of the region. 

The temple has a large pond by it. The pond is home to large varities of turtles and  fishes. Some turtles are believed to be hundreds of years old. The temple campus also has peacock, deer, pythons etc. These animals along with the temple draw attraction of the tourists.