The 34-year-old was caught on Thursday night with seven kilograms of cocaine in her luggage.
She was arrested after the Thai customs department received a tip-off that a foreign national planned to smuggle drugs into Thailand.
The cocaine had been stashed in chocolate boxes.
The accused has denied any knowledge of the drugs, claiming instead that she had travelled to Thailand to buy clothes to sell in South Africa.
She told authorities that a friend had given her the chocolate boxes to pass on to a fellow South African in Thailand.
Thai officials have addressed a news conference about the arrest.