Nigeria has strongly criticised a survey which ranks it as the most corrupt country in Africa saying it is "fundamentally flawed".
Nigeria has saved money by opening public contracts to competition
Finance Minister Ngozi Okonjo-Iweala said Transparency International failed to take into account efforts to fight corruption.
Nicknamed Nigeria's "Corruption Cop" by local media, she said ending corruption takes time.
Out of the 146 countries, only Haiti and Bangladesh were rated more corrupt.
Ms Okonjo-Iweala said the Berlin-based organisation's methodology was too backward looking and was "not particularly helpful".
"If you're doing reforms it's important that the new moves being made are recognised," she told the BBC's Network Africa programme.
Over the last year, she said, Nigeria's President Olusegun Obasanjo had instituted many measures to curb corruption including reforms to contract procurements and bidding.
She denied that the various anti-corruption bodies set up by the president were underfunded.
There was adequate provision for them in this year's budget and the agencies were benefiting from donor funding, she said.
"We're doing a lot about corruption... it takes a long time and we are doing the right measures."
It took 20 years for the system under successive military governments to become so corrupt, so it will take time to bring it under control, she said.