70-year-old Nunu Devi was first beaten up and a part of her nose was chopped off in Kainzari village in Khagaria district, about 200 km from the state capital Patna.
The woman was seriously injured in the incident and as admitted to a hospital.
Deputy Superintendent of Police Ashok Kumar Singh said five people have been booked for the crime. All the accused were on the run, he said.
According to the police, some villagers blamed the woman, an elected Sarpanch (headwoman) of the village, for the illness of two people and said she practiced witchcraft.
They asked her to cure the two. When she said she could not do it, they attacked her with bamboo and iron sticks.
The practice of branding women as witches and torturing them - often to death - continues unabated in rural Bihar.
Some months ago, a woman in Sitamarhi district was forced to eat human excreta after villagers branded her a witch.
Last year, the Bihar Human Rights Commission had directed the government to expedite probe and trial in cases related to offences under the Prevention of Witch Hunting Act, 1999.
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