The Federal Government will lobby against the death penalty handed down to an Australian man convicted in Vietnam for conspiring to smuggle heroin.

Mai Cong Thanh, 46, was sentenced to death by firing squad on Thursday in Ho Chi Minh's People's Court - two years after his arrest - for conspiring with two other Australians to smuggle 1.7 kilograms of heroin from Vietnam to Australia in loudspeaker systems.

Thanh and Nguyen Manh Cuong were arrested in June 2003 after small packets of compressed heroin were found in 76 stereo speakers during a raid on their rented workshop, according to state-controlled media. The speakers were among 306 to be shipped from Vietnam to Australia.

Cuong was found mentally unfit to stand trial. A third man is understood to have escaped to Australia. Under Vietnamese law, the death penalty can be imposed for heroin amounts over 100 grams. For amounts over 600 grams it is almost certain the death penalty will be applied.

Vietnam launched a nationwide crackdown on prostitution and drug abuse earlier this month.

In April, Australian Nguyen Van Chinh was sentenced to death for trafficking heroin, and another Australian, Tony Tran, received a 20-year jail sentence earlier this month.

Foreign Minister Alexander Downer today said he was hopeful Vietnam will spare two Australians from the death penalty following a meeting with his Vietnamese counterpart.

Mr Downer met with Nguyen Dy Nien ahead of a regional security meeting in Laos.

After the talks he said he "hopeful without being overly optimistic" that the pair would be granted clemency by Vietnam's president.

"They have exercised clemency as a result of representations that I have made on one previous occasion," he said.

A 45-year-old Australian of Vietnamese origin, Nguyen Van Chinh, recently lost his appeal against his death sentence for trafficking heroin in Vietnam.

Chinh was found guilty in April of buying 1.05kg of heroin to send abroad and was sentenced to death by firing squad.

Only a presidential pardon can save him from execution.

Melbourne man Mai Cong Thanh, a 46-year-old Vietnamese Australian, is also on death row after being sentenced to death in Ho Chi Minh City for attempting to send nearly 2kg of heroin to Australia stuffed in loudspeakers.

Since 1975 Vietnam has executed only one westerner.

AAP