The incident occurred at 9:30 in the morning while the woman was walking her dog at Sea Pines Resort; the alligator attacked Cassandra Cline and pulled her underwater.
"She was walking the dog near the lagoon and the alligator came out of the water and tried to get the dog," South Carolina Department of Natural Resources spokesman David Lucas said. "The lady tried to rescue the dog and a maintenance worker ran over to help."
The dog did not appear to be injured during the incident, officials said.
Sea Pines Resort relayed news of the tragedy via its Facebook page, writing "We are shocked and heartbroken over this loss and are praying for Ms.Cline's family and loved ones during this difficult time."
The reptile was later found and killed, according to Lucas, as cited by CBS News.