The woman's granddaughter heard strange noises coming from the OAP's room and raced to help.
Family members dragged 20-year-old Argha Biswas from under the woman's bed and handed him over to police.
The suspect was reportedly drunk when he was found in the elderly woman's home in the village of Chakulia in Nadia, West Bengal.
The alleged assault took place on Tuesday, October 23 when the victim was home alone.
The woman's granddaughter, who has not been named, said: "I heard some strange noises but when I looked through the window, I immediately called others to help when I saw my grandmother."
The Indian police immediately arrested the suspect and after an initial court hearing, he is now in 14 days judicial custody before another hearing takes place.
Biswas told reporters outside the court that he was under the influence of alcohol and did not know what he was doing.
The 100-year-old woman was taken to a hospital following the alleged incident but was discharged in Wednesday.
Rupesh Kumar, a senior police officer, said: "She was sleeping alone in her home.
The house wasn't locked as the village culture.
"Her family members found the man when she cried for help.
"When we arrived, we found Argha Biswas under the bed, he was caught by the family members of the old woman."