"The cub is robust, fully formed and is a bright, healthy shade of pink," the zoo said in a statement.
The cub was born Friday to Mei Xiang, a giant panda. A day later, on Saturday, Mei Xiang delivered a second cub that was stillborn.
Zookeepers attempted Saturday without success to distract Mei Xiang for long enough to get her living cub away from her for a short examination. They succeeded just before 9 a.m. Sunday.
The newborn weighs 137 grams (4.8 ounces), the zoo said. The heart rate was steady during the exam, the cub was using both lungs to breath and it had a full stomach, suggesting it has been nursing and digesting well.
Both keepers and veterinarians described the newborn as "healthy, active and vibrant." But they said it is too small to determine whether it is male or female yet.
When Meii Xiang delivered the stillborn cub, 26 hours after giving birth, keepers said she spent more than 15 minutes grooming and stroking the tiny corpse before allowing it to fall to the floor. The Washington Post reported. A device was used to grab the cub for a necropsy.
The cub was not fully developed, keepers said.
Mei Xiang gave birth to a male cub, Tai Shan, in 2005. He was sent to a breeding program in China in 2010.
In September last year she bore a female who died six days after birth.