On the 2012 Transparency International Corruption Perceptions Index, it shares first place with Denmark and New Zealand.
This year's index, published on Wednesday, measures perceived levels of graft in the public sector in 176 countries.
Finland topped the list several times before dropping to sixth in 2009 amid the campaign finance scandal. Last year it was ranked second along with Denmark, just behind New Zealand.
At the bottom of this year's list are Afghanistan, North Korea and Somalia.
Eurozone crisis worsened by graft
The anti-graft watchdog Transparency International has published the list annually since 1995.
This year it warns that the nations hardest hit by the eurozone debt crisis are being held back by an inability to get to grips with corruption.
The Berlin-based body ranked Greece and Italy at places 94 and 72 respectively, and called for Europe to make tackling corruption a top priority in its battle against the crisis. Perceived corruption in both countries appeared to have worsened.
Among other major nations, the United States came in 19th, just behind Japan and Britain, which were 17th equal.