Vimla Devi was killed by her son Promod Kumar yesterday in Jivna village of the district. The youth later threw the body into a Ganga canal, police said.
Kumar, who was arrested, has confessed to his crime, they added.
Irate women protested against the murder and pelted stones on the police vehicle in which the accused was brought.
The body of the victim has not yet been recovered from the canal.