Legalising voluntary euthanasia is a slippery slope towards the kinds of atrocities that were carried out in Nazi Germany, a Liberal MP has told South Australia's Parliament.

Parliament has been debating Labor MP Steph Key's private member's bill that seeks to allow voluntary euthanasia under certain circumstances.

Liberal MP Adrian Pederick told Parliament he was strongly opposed to the move.

He used the example of a conversation he had with a woman around euthanasia who asked how aged care would be funded in the future.

"That put really big alarm bells inside my head and I said to her, 'If that is your reason for promoting voluntary euthanasia, I cannot live with that'," Mr Pederick told Parliament.

"I mean this is the sort of thing that was done in the 40s in Nazi Germany.

"I just feel that comments like that do lead us down a slippery slope.

"I will stand fast in opposing this legislation in regards to voluntary euthanasia."

The bill has the support of Liberal MP Duncan McFetridge.

MPs will have a conscience vote on the bill.