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.
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