The International Rhino Foundation said the female calf was born yesterday, weighs about 20 kilograms and looks healthy and active.
"We haven't stopped smiling since the moment we were sure she was alive and healthy," said IRF's executive director Susie Ellis in a statement. "While one birth does not save the species, it's one more Sumatran rhino on Earth."
Only an estimated 100 Sumatran rhinos remain, mostly on the island of Sumatra, and nine are in captivity.
The species was rediscovered in the Indonesian part of Borneo through their trails and footprints in 2013.
The calf is the second to its mother Ratu, who gave birth to a male named Andatu in 2012.