The woman, named locally as 24-year-old Li Zhenghua, was found trying to eat the child while in a hospital ward in Shenzhen, southern China, recovering from the birth.
Luckily a nurse saw the woman with her teeth locked around her son and raised the alarm.
The nurse, named as Liu Tianlun, attempted to prise the woman off the baby but the mother refused to let her child go.
She was eventually sedated and extracted from the baby.
A hospital spokesman said: ‘It was really shocking, the arm was badly damaged and suffered not only heavy bruising but bleeding as a result of the bite.
‘Fortunately, doctors managed to insert something to stop her closing her teeth and then levered her jaws apart.
‘After that they gave her a sedative and took the baby to a secure location.’
The mother is believed to have been living on the street after being thrown out by her mother-in-law despite being pregnant.
She is believed to have been surviving on the streets for a number of weeks before going into labour and being taken to hospital.
Hospital staff are deciding whether to give the newborn back to his mother.
An investigation into the incident is ongoing.