Mr Tutu has been receiving treatment for “a persistent infection”, a statement on his official website says.
The 83-year-old Nobel peace laureate cancelled a planned trip to Rome in December following another infection.
Mr Tutu retired from public life in 2011 but continues to travel widely.
It is not known whether the admission is linked to Mr Tutu’s treatment for prostate cancer, which he has afflicted him for more than a decade.
His hospitalization comes a few days after he renewed his wedding vows to his wife Leah Tutu to mark their 60th wedding anniversary.