Neighbours raised the alarm after witnesses had seen her being attacked by her son in the stairwell and in the garden where they live in Gothenburg.
She had been heard screaming that she'd been struck with a hammer and was attempting to make an escape when police were notified.
Local police said that the woman was struck between four and five times in the head with sharp blows. She was transferred to the Sahlgrenska hospital nursing extensive head injuries and had also lost a number of teeth following the assault.
The local newspaper Göteborgs Posten said that the woman's life was not in danger.
Police said that the boy was arrested within 45 minutes after being found at another address in the neighbourhood.
"The arrest was undramatic," said police spokesperson Björ Blixter to the Göteborgs Posten who added that the hammer had been seized and confiscated.
"We don't yet know anything regarding the motive for this," Blixter told the TT news agency.
A preliminary investigation into the aggravated assault is already under way.
Meanwhile, in Malmö an 18-year-old man has been taken to hospital with serious injuries after he was stabbed at an apartment in the city.
He was attending a party in the apartment when the stabbing took place. Police have classified the incident as attempted murder and already interviewed several people but, as yet, there are no suspects.
The man's condition is reported to be stable in hospital reports Sydsvenskan.