The 84-year-old woman was molested on April 20 by her neighbour when she was alone at her sister's house at Chavara in Kollam district where she was staying, police said.
The incident came to light after the health of the old woman, who was already sick, deteriorated and she was admitted to the Medical college Hospital where she died yesterday, police said.
A post-mortem revealed that she had been molested, they added.