The toddler fell from a flat on Lewiston Drive in Summerston, just after 5pm on Thursday.
The three-year-old boy was rushed Queen Elizabeth University Hospital following the incident. He is thought to be in a serious condition.
A Police Scotland spokeswoman said: “On Thursday, police received a report of a three-year-old boy having fallen from a window on Lewiston Drive.
“The boy was taken to Queen Elizabeth Hospital where he is in a serious condition.
“Inquiries are ongoing to establish the circumstances of the incident.”
A Scottish Ambulance Service spokesman added: “We dispatched one ambulance, a paramedic response unit, our special operations response team and the trauma team.
“The first unit arrived on scene within six minutes.”