Archbishop Tutu thanked “everyone who had sent love and prayers” since his admission to hospital in Cape Town, his daughter Reverend Mpho Tutu said.
The family hopes he will be able to return home “in a day or two”, his daughter said in an earlier statement.
He retired from public life in 2011 but continues to travel widely.
The 83-year-old Nobel peace laureate cancelled a planned trip to Rome in December following another infection.
The admission is not thought to be linked to Archbishop Tutu’s treatment for prostate cancer, which 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.