Transparency International's Corruption Perceptions Index 2013, which was released today, shows Australia at ninth place, down two places from last year.
Australia's score has also dropped from 85 in 2012 to 81 this year.
Transparency International Australia’s executive director Michael Ahrens told SBS the results were dramatic.
“It’s very rare to drop in such a way,” he said.
Mr Ahrens attributed the decline to the prosecution of Securency and Note Printing Australia executives, and the findings of ICAC in relation to Eddie Obeid and corruption in the NSW state government.
The index ranks 177 countries on a scale from 100 (the least corrupt) to zero (the most corrupt).
Denmark and New Zealand were placed first equal, with a score of 91.
Other countries to show significant decline include Syria, Yemen and Libya due to ongoing conflicts in those areas.
Afghanistan, North Korea and Somalia shared the last place, with scores of eight each.
Mr Ahrens said countries' scores were more important than their rankings, which could change depending on the performance of countries above them.
He said corruption was often shrouded in secrecy so formulating the index could be challenging.
"Rampant corruption is deliberately hidden, So that’s why it’s the revelations of investigative journalists we reply upon," he said.
"We are no less corrupt now then ICAC but the fact that these things happen mean that we understand it...the realisation that these things can and do go on."
Mr Ahrens predicted Australia would continue to decline into next year’s index because of ongoing issues relating to the corruption of customs officials.
He said the index was scrutinised by foreign investors and had an "enormous" impact on countries' reputations around the world.
"Big mining countries have a look at these indexes every time they look at a new phase of development," he said.
The index, which measures perceptions of corruption, is based on experts' opinions of public-sector corruption.
Transparency and easy access to information can bolster countries' scores while a lack of accountability in the public sector can damage them.