Investigators believe the woman was riding the Honda motorcycle that she purchased just four days ago from Chalong Circle in southern Phuket to Karon, on the island's west coast.
She was in a winding stretch of Patak Road and probably travelling too fast when the motorcycle skidded on sand on the road surface.
She was thrown onto the safety railing, and died immediately.
The railing is designed to prevent heavier vehicles from leaving the surface of the road. But it proved fatal for the motorcycle rider today.
She was 25 years old and worked as a kitchen assistant in a resort in Karon. Her body was taken to Vachira Phuket Hospital, in Phuket City.