Sinn Fein generated almost three times more money than its political rivals last year and outspent them twice over.
With an annual income of just under £1.2 million for 2009 - the year of the European election campaign - Sinn Fein was streets ahead of second-placed SDLP (£400,000), figures from the Electoral Commission showed.
The republican party, whose elected representatives donate a proportion of their wages into the coffers, spent around £6,000 more than it brought in.
The DUP spent £480,000 while it only generated £350,000. The SDLP also posted a considerable loss, spending £500,000 - £100,000 more than its income - and the nationalists will face another outgoing soon, after being fined by the commission for failing to provide an auditor's report with one unit of its accounts.
Buoyed by its alliance with the Conservative party, the UUP was the only party to stay in the black - generating £390,000 and spending £357,000.
Seamus Magee, head of the Electoral Commission's Northern Ireland office, said: "The rules that we regulate demand that political parties, who play a crucial part in our democracy, are transparent about how much money they raise and how they spend it.
"Their annual statements of accounts help give that picture.
"Being able to view the accounts of a political party is particularly important in Northern Ireland as it is the only source of information for anyone wishing to find out more about a political party's finances.
"All parties submitted their accounts on time; and one accounting unit made what we hope will prove to be a one-off mistake but will face a fine for late submission."