Nguyen Thi Phuong Thao, 23, was arrested by the police on Thursday.
Thao, an employee at a karaoke parlor, lives with her two young children in Tan Dinh Ward.
At around 7:30 p.m. on May 16 she returned home high on liquor and drugs and went to sleep when her child started crying. She tried to put him to sleep but failed, and, angered, beat him before going back to sleep.
At 11 p.m. she woke up and discovered that the child had stopped breathing. She rushed him to hospital but in vain.
A preliminary investigation showed that the boy had multiple injuries, which were the possible cause of death.