The 94-year-old was hospitalised “due to the recurrence of his lung infection” just before midnight on Wednesday, President Jacob Zuma’s office said in a statement.
It is the second time this month that the anti-apartheid hero has spent the night in hospital and follows a nearly three-week stay in December for the lung infection and for surgery to extract gallstones.
Earlier this month, he spent a night in hospital for a “scheduled medical checkup”.
“Doctors are attending to him, ensuring that he has the best possible expert medical treatment and comfort,” said the presidency.
Zuma wished “Madiba”, as he is fondly known in South Africa, a quick recovery.
“We appeal to the people of South Africa and the world to pray for our beloved Madiba and his family and to keep them in their thoughts,” he said.
“We have full confidence in the medical team and know that they will do everything possible to ensure recovery.”
The name or location of the hospital was not provided.
Mandela has had several health scares over the years.
In early 2012, he was admitted for a minor exploratory procedure to investigate persistent abdominal pain.
In 2011, he was hospitalised for two nights for an unnamed acute respiratory infection.
The Nobel Peace Prize winner diagnosed with early stage tuberculosis in 1988 while serving a 27-year jail term during apartheid.