Lun Lun, a 15-year-old giant panda, gave birth to the cubs on Monday.
An ultrasound confirmed her pregnancy in June but officials said they were unaware she was having twins until the second cub was born minutes after the first.
The cubs are the first giant panda twins born in the US since 1987.
Zoo Atlanta's deputy director, Dwight Lawson, said both cubs appear to be healthy.
But officials are taking precautions because of a high infant mortality rate among baby pandas.
The cubs will not be named until they are 100 days old, in keeping with a Chinese tradition, Mr Lawson said.
COMMENT RULES: Comments that are judged to be defamatory, abusive or in bad taste are not acceptable and contributors who consistently fall below certain criteria will be permanently blacklisted. The moderator will not enter into debate with individual contributors and the moderator’s decision is final. It is Belfast Telegraph policy to close comments on court cases, tribunals and active legal investigations. We may also close comments on articles which are being targeted for abuse. Problems with commenting? email@example.com