Ireland has slumped five places to 19th in Transparency International's latest Corruption Perceptions Index.
The CPI looks at anti-corruption laws, access to information and conflicts of interest. It ranks countries from zero-ten, with zero being highly corrupt and ten being very clean.
Last year, Ireland was ranked 14 out of 183 countries with a score of eight, this year it is ranked 19th with a score of 7.5 – tied with Belgium.
New Zealand is seen as the least-corrupt country, with a score of 9.5, followed by Denmark, Finland and Sweden.
Somalia and North Korea are tied for last place.
Top 20 countries
1 New Zealand
2 Denmark
2 Finland
4 Sweden
5 Singapore
6 Norway
7 Netherlands
8 Australia
8 Switzerland
10 Canada
11 Luxembourg
12 Hong Kong
13 Iceland
14 Germany
14 Japan
16 Austria
16 Barbados
16 United Kingdom
19 Belgium
19 Ireland
Transparency International Ireland's chief executive John Devitt said the slip could deter international investment.
"Ireland's reputation has been tarnished by the banking crisis which exposed a cosy-cartel culture involving bankers, business elites and politicians," he said.
"This same pernicious culture brought us the Moriarty Tribunal, the Planning Tribunal, the DIRT inquiry and more.
"The country's international reputation now rests as much on our leaders' commitment to open up government and uphold the rule of law as it does on fixing our economy."
