Foreign Minister Alexander Downer says he is very concerned about an Australian on trial for heroin trafficking in Singapore.

Melbourne man Nguyen Tuong Van is facing a death penalty if he is found guilty of trying to board a Qantas flight two years ago carrying almost 400 grams of heroin.

Under Singapore law a mandatory death sentence applies to anyone caught with more than 15 grams of heroin.

Mr Downer says he has been trying to convince the Singapore Government to spare Toung Van's life if he is found guilty.

"Number one of course there's an appeals process and number two the President of Singapore has the power to exercise clemency," he said.

"But by the way, I think I'm right in saying ever since the foundation of modern Singapore the President's only exercised clemency on five or six occasions.

"Don't hold me to that, but on very few occasions."

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