The Federal Government has lodged an appeal against a decision not to extradite an elderly Perth man wanted for questioning over alleged war crimes.

Hungarian military authorities want to question former Hungarian soldier Charles Zentai, now 89, over the murder of an 18-year-old Jewish man in Nazi-occupied Hungary in 1944.

Home Affairs Minister Brendan O'Connor approved the extradition in 2009 but it was overturned last year by the Federal Court.

Mr Zentai, who is now an Australian citizen, has consistently declared his innocence.

"My father is quite devastated by the decision by the minister to appeal and the rest of our family also," his son Ernie Steiner said.

"We were hoping that this matter would have concluded by now and it's a big disappointment."

Ernie Steiner says his father is willing to speak to Hungarian officials in Australia.

"It just seems that this whole process that's taking place now is so unnecessary," he said.

"It's very expensive and why they're going down this avenue, I really don't know."

Ernie Steiner says according to his own investigations, the main evidence against his father is from statements made by people implicated in the murder.

"It came from a corrupt people's court system and those men had been tortured for their statements and that is in the documents we've got," he said.

"This process could take a long time. For him to end his days potentially while on bail is absolutely disgraceful."

Ernie Steiner says his father's health is deteriorating and the decision could mean he is faced with the prospect of extradition for the rest of his life.

The Simon Wiesenthal Centre, the US-based organisation investigating the history of the Holocaust, has welcomed the news of the Federal Government's decision to appeal.

"That is the correct response by the Australian Government which should be commended for its perseverance in this case," spokesman Efraim Zuroff said.

"His fate should be decided in a court in Hungary which is a full-fledged member of the EU.

"The sooner that he is sent to Budapest to face trial, the better everyone will be."

The appeal will be heard in the Full Federal Court on a date to be fixed.

abc.net.au