The body of Mira Basu, 67, was found lying in a government apartment in Paikpara on Tuesday after neighbours alerted police about a foul smell emanating from the dwelling.
Anirban Basu, her son, was oblivious to the fact that she had died and was staying in another room, police said.
"He is mentally unstable. We guess he did not know his mother had died as he always used to keep himself locked in his room," a neighbour said.
"No one was aware of the death as both had very little contact with the outside world," he added.
The incident is a grim reminder of a 2015 incident in Kolkata's Robinson Street where middle-aged Partha De was found living in his house with the skeletons of his sister Debjani and two Labrador dogs.