Emergency services rushed to the sheer drop at around 5pm after reports of a child falling from height.
The boy, aged 10, was found to have suffered serious injuries and was airlifted to St George’s Hospital, in south London, where he remains.
He is not local to the area and is believed to have been visiting Brighton and Hove with his family.
There is a security fence that runs across the top of the cliff face.
Enquiries to understand how the boy fell from the cliff are ongoing and his family are receiving support from officers.
In a statement Sussex Police said: “Police responded to a report of a boy falling from height in Ovingdean, at about 5pm on Saturday September 24.
“The boy was found to have suffered serious injuries and was airlifted to hospital, where he remains critically ill. He is not local to the area and was visiting Brighton & Hove.
“Ovingdean roundabout was closed whilst the boy was bought to safety. The roundabout re-opened just before 10pm.
“We thank the public for their patience during the closure. The boy and his family are receiving support from officers and enquiries are continuing.”
