According to police, victim Saraswati Keer had been bedridden for the past several years due to bad health.
Last night, accused Ram Keer reached his house in Shanidev building in Colaba in a drunken state and began arguing with his wife.
He began thrashing his ailing mother with a stick after his wife ran out of the house fearing his wrath, police said adding when the wife returned home along with neighbours, the old lady was in unconscious state.
The elderly woman was taken to a nearby hospital where she was declared dead this morning, police said.