Lam Thi Kim Hong Hanh, 38, was caught with 376 grams (13 ounces) of the drug at Ho Chi Minh city's Tan Son Nhat airport in December last year, the Cong An Nhan Dan newspaper reported on its website.
Hanh told the court she was planning to transport the drugs from Vietnam to Australia for a fee of USD 3,480.
The court in the southern Vietnamese city "sentenced her to 20 years imprisonment for the charge of illegal transport of drugs", the Cong An Nhan Dan said.
Convictions and sentences are usually revealed only by local media, which is strictly under state control.
The "Golden Triangle" region covering part of Myanmar, Laos and Thailand was once the world's top source of opium but has been overtaken by Afghanistan.
Vietnam has sentenced dozens of foreigners to death for drug offences -- many of them Australian nationals of Vietnamese origin -- but it has been decades since a foreign national was executed in the country.
Despite the harsh sentencing, drug smuggling and use is still commonplace.
In July police arrested 17 people after a blitz on drug crime uncovered major stashes of heroin, cannabis and precursor chemicals.
