The incident, which occurred last night, came to light when the woman's daughter returned home from a temple festival this morning and found her mother with injuries on her body, police said.
A 24-year-old man living in the same area has been arrested in connection with the incident, they said.
The man had forcibly entered the house and allegedly sexually assaulted her. He has been booked under various IPC sections, including 376 (punishment for rape), police said.
The elderly woman has been hospitalised.