Japan's Foreign Minister Seiji Maehara has resigned after being criticised for accepting a political donation from a foreign national.
Japanese law bans the practise, if done intentionally, and the opposition had called on him to quit.
The move is seen as a blow to Prime Minister Naoto Kan, who has been struggling to get budget bills through parliament and keep onto his own job.
Mr Maehara had been seen as a potential successor to Mr Kan.
On Friday, he admitted taking a 50,000 yen ($610) political donation from a South Korean national resident in Japan.
PM under pressure
The sum is small but Japanese law bars politicians from accepting money from outsiders to prevent foreign powers having influence on domestic politics.
The opposition said Mr Maehara's position was untenable.
"I apologise to the Japanese people for stepping down after only six months and provoking distrust over a problem with my political funding, although I have sought to pursue a clean style of politics," Mr Maehara said announcing his decision to step down.
Even before the scandal, Mr Kan was battling to stave off opposition calls for an early general election, says the BBC's Roland Buerk in Tokyo.
He wants to implement tax reform to cover the costs of Japan's rapidly ageing society and rein in its massive public debt.
But deadlock in parliament means Mr Kan is struggling to pass bills to implement the trillion- dollar budget for the new financial year which begins next month.
The foreign minister had called for closer ties with the US and had been critical of China's military build-up.