The two women, who sold crabs near Hon Rom Beach, went swimming at around 5 pm on Monday.
Residents later spotted them struggling in the water and rushed to help.
Both were brought ashore in critical condition. One died shortly after being pulled from the water, while the other could not be revived despite first aid.
No large waves were reported at the time, but local fishermen said a strong current pulling away from shore could be seen on the surface.
Mui Ne police arrived at the scene and are investigating the cause of the incident.