Female calf Wasswa was born first May 10, followed by brother Nakato.
Officials with the Natural Bridge Wildlife Ranch waited until Tuesday to announce the births to ensure the calves would survive.
Ranch spokeswoman Melissa Welch says Wasswa and Nakato are the only set of living giraffe twins in the U.S.
A previous set was born in 1988 but have since died.
Welch says most twin giraffes are stillborn or have to be aborted.
Wasswa and Nakato are reticulated giraffes, one of the most common species.
They'll stay at the privately owned ranch outside New Braunfels for public viewing.