Rajkali Devi was attacked in Redia village with traditional weapons and a part of her tongue was cut off leaving her seriously injured, Tilauthu police station in-charge Pramod Kumar said.
The Dalit widow was admitted to a hospital and a First Information Report was registered on Sunday on the complaint by her granddaughter.
The granddaughter, who was sleeping with Rajkali Devi, at the time of the attack said three villagers forcibly entered their house late on Saturday and chopped off her grandmother's tongue accusing her of practicing witchcraft.
A man hunt was underway to nab the culprits.
Branding women as witches and torturing them -- often to death -- continues to prevail in parts of rural Bihar.
The Bihar Human Rights Commission had been asking the government to expedite probes and trials in cases related to offences under the Prevention of Witch Hunting Act, 1999