Mr Bossi has been in Italian politics since the late 1980s
Leading Italian populist politician Umberto Bossi has resigned as head of the Northern League after a financial scandal engulfed the party.
The Northern League is the only party in opposition to the current technocratic government led by Prime Minister Mario Monti.
A former party treasurer is suspected of misusing funds.
Mr Bossi, known as a fierce critic of corruption in public life, denies any wrongdoing himself.
Northern League treasurer Francesco Belsito resigned on Tuesday after prosecutors alleged he had used party funds to pay for, among other things, the remodelling of Mr Bossi’s villa and holidays for the leader’s children.
There was no immediate comment from the former treasurer on the accusations laid against him.
News of Mr Bossi’s resignation emerged on Thursday, with no comment from the leader himself.
The scandal has been all the more embarrassing for him because he has always been bitterly contemptuous of the corruption that plagues so much of Italian public life, the BBC’s Alan Johnston reports from Rome.
Mr Bossi has been one of the most colourful figures on the Italian political stage, coming to prominence on a separatist platform, our correspondent says.
In fiery speeches he frequently criticised “the corrupt and lazy South” for draining hard-earned wealth away from the North.
Mr Bossi once described the European Union as a nest of communist bankers and freemasons.
Despite the rhetoric, the Northern League formed coalition governments with the right-wing parties supporting the governments of Prime Minister Silvio Berlusconi.
Following his resignation the party instantly gave him the honorary position of president.
But Alan Johnston says the amount of influence Mr Bossi may wield in future will perhaps depend on how the current fraud inquiry plays out.