It is the second such penalty given to a foreigner within a week in the communist country, and the second death sentence handed to a Thai woman in 14 months.
A People's Court judge in Ho Chi Minh City, reflecting enforcement of some of the toughest drug laws in the world, sentenced Suracha Chaimongkol to death after she was caught carrying 2 kilogrammes of cocaine, the Thanh Nien (Youth) newspaper said.
The drugs were discovered hidden inside two photograph albums when the 31-year-old graduate landed at Ho Chi Minh City's airport in October last year after taking a flight from Brazil.
Shortly after the Vietnamese court's death sentence, Manasvi Srisodapol, Foreign Affairs Ministry spokesman, said the consulate-general in Ho Chi Minh had sent someone to attend the court's ruling on Tuesday.
Mr Manasvi said Suracha could appeal to the Supreme People's Court of Vietnam within 15 days or she could ask for a pardon from the Vietnamese president within seven days from the date of the ruling.
Mr Manasvi said the consulate-general in Ho Chi Minh City has sent a letter to Vietnamese authorities asking them to allow Thai diplomats to visit Suracha so they could inform her of her legal rights and options.
On Monday, state media said a 31-year-old Nigerian man was sentenced to death by the same court in the southern business hub for smuggling 3.4kg of methamphetamines from Qatar into Vietnam.
Vietnam takes a hard line on drugs and anyone found guilty of attempting to smuggle more than 100 grammes of heroin or cocaine can face the death penalty.
Convictions and sentences are revealed only by local media which is under strict state control.
Suracha told the court she did not know she was carrying the drugs, but said she had been paid to bring the photograph albums to Vietnam, according to the Thanh Nien report.
After a two-year hiatus in carrying out capital punishment because of problems procuring chemicals for lethal injections, Vietnam executed its first prisoner using the method earlier this month.
The country has more than 586 prisoners on death row, at least 117 of whom meet all of the criteria for immediate execution, media reports have said.
Although the country does not release statistics on executions, rights group Amnesty International recorded five executions in 2011 and said 23 new death sentences were handed out that year, mainly to drug traffickers.
Foreigners frequently fall foul of the nation's stiff drug laws.
In June last year, Thai design student Preeyanooch Phuttharaksa, 23, was handed the death penalty for trafficking 3kg of methamphetamine by the Ho Chi Minh City court, while in October, a 61-year-old Filipina received the death penalty for smuggling 5kg of methamphetamines.
Preeyanooch, who appealed to the president for clemency, had a story almost identical to that of Suracha. She made a bad choice when she began smuggling drugs for a Benin-based drug gang. She was caught in Vietnam on her third trafficking trip.