The incident happened in Hatsingimari village in the South Salmara district.
According to locals, the younger brother accidentally fell into the river, and was carried away by the powerful currents. The older brother valiantly leapt into the river to help him but was also carried away.
The two, who are said to be in their teens, vanished shortly and were never discovered.
They have been identified as Golam Mustafa and Dilwar Hussain.
Local police and the State Disaster Response Funds (SDRF) rushed to the location after learning about the incident and started a search operation for the two missing teenagers.
Following an extensive search, the bodies were later found.
Earlier on Sunday, three school students drowned in the River Brahmaputra in North Guwahati during the Bihu celebrations.
According to police, the students were taking a bath in the Mariapatty area in the late afternoon and tragically perished after drowning.
After being taken to a neighbouring hospital, all the three were decalred dead due to drowning.
IANS