Driscoll Children's Hospital spokesman Jeff Salzgeber says the hours-long operation began Tuesday morning.
PHOTOS: Surgery separates infant conjoined twins
Ximena and Scarlett Hernandez-Torres shared a colon and bladders that will be reconstructed. Their identical triplet sister, Catalina, was born without serious health issues.
The hospital staff has cared for the conjoined girls since they were transferred to the Corpus Christi facility hours after birth.
Dr. Haroon Patel says a team of specialists had been working for months to prepare for the surgery, which lasted about 15 hours.
A hospital statement says doctors have a positive outlook for the children's recovery. The girls will require additional surgeries as they grow.