"Afghanistan has been tarnished by administrative corruption, and I will launch a campaign to clean the government of corruption," he said after winning a second term when a runoff election was canceled because his rival, Abdullah Abdullah, dropped out of the race.
Karzai was not specific about whether he would replace ministers and officials.
"The problems cannot be solved by changing high-ranking officials. We'll review the laws and see what problems are in the law, and we will draft some new laws," The New York Times quoted him as saying.
Karzai's cabinet and campaign staff attended the news conference and he was flanked by Vice Presidents Karim Khalili and Marshal Muhammad Qasim Fahim, The Times said, adding Marshal Fahim is among powerful Afghans accused by the international community of abuses.
Karzai's half-brother, Ahmed Wali Karzai, a powerful figure in south Afghanistan, also has been of accused of drug trafficking.
The president told reporters he planned to strengthen an anti-corruption commission that was set up last year.
He is expected to reach out to Abdullah to try and bring in some of his supporters, the newspaper said.